Karl Marx Hates Your Guts

Karl Marx Hates Your Guts is the inverse of Adam Smith Hates Your Guts. Goods are available and distributed at the same monetary rate everywhere. "Buy Low, Sell High" doesn't apply in such a place. Prices are fixed in such a way that it is impossible to make money by buying something and then re-selling it elsewhere.

This becomes a problem in these situations:
 * 1) A Businessman Is You. Try to make a profit in this immovable market.
 * 2) The only way to earn money is via Money Spider. If speculation is unprofitable, upgrading equipment becomes dangerous.

This applies only to games or stories where you could make a living as a businessman if the game did not set up prices in precisely the right way as to make this impossible. The trope is named after Karl Marx, one of the founders of modern communism.

This can also, ironically, overlap with Adam Smith Hates Your Guts when there is both a single price no matter where you go and that price rises as you move along (or a variation on that scheme).

This is somewhat Truth in Television as the act of arbitrage will cause prices in various areas to move to one price (the so-called law of one price). However, the way this is handled in games makes this somewhat infuriating, particularly when prices should be different despite arbitrage (or because arbitrage can't happen). For instance, having prices for a night at the inn fixed across the empire makes no sense if one inn is in the Capital City and another is in some village nobody has ever heard of.

MMORPGs

 * In World of Warcraft, vendors pay 25% of the selling price of an item, if you're allowed to vendor it at all, and all vendor-bought items cost the same everywhere (subject to reputation discounts). Sources of income are quests and Money Spiders. That said, the player-driven economy is vibrant and can be highly profitable.
 * The majority of MMORPGs will have NPCs pay the same price for the same item regardless of location. In the few games that vary store prices with location or a review of the current (in-game) economic situation, arbitrage becomes a common if rather inefficient source of income for players -- though merchant classes can usually squeeze more out of it due to trade being their main activity and prices don't fluctuate as much as in Real Life if they change at all.

Roguelike

 * Currently averted in Dwarf Fortress, as the economy system is disabled and pending a significant retooling. It's played straight in earlier versions, where all prices are fixed no matter where you are, based entirely on material and quality, and every non-worthless item has a minimum value of 1. So while you can't turn a profit on bought goods, even if they're from the other end of the world, you can make money selling found/stolen goods even if they're literally found in infinite quantities laying around on the ground in front of the buyer. The newly begun Caravan development arc is largely based on averting this by implementing a value system based on the availability of goods in the area involved.

Role Playing Game

 * Completely averted in the latest Atelier series game: Atelier Lina. The price of goods fluctuates year round, and buying stuff in one town to sell in another town is the fastest, easiest and most profitable way to make obscene amounts of cash in a very short amount of time.
 * Averted in Paper Mario, where it's possible to buy items in one town and sell them at another town for a profit. One of the possible ways to do this is told to you as payment for a side quest. "Go to Petalburg, buy a Sleepy Sheep, go to Rogueport, and sell the Sleepy Sheep for a two-coin profit!"
 * Using logic and the principle of supply and demand and how it affects price, this can be cranked Up to Eleven. In Keelhaul Key, buy Fire Flowers. Sell them in Fahr Outpost for a 3-coin profit. Before leaving, buy Ice Storms, which sell for a 4-coin profit in Keelhaul Key. It's easy to make money in the late game without killing enemies for it.
 * Partly averted in all Suikoden games since II with regard to trade goods, where you can buy low in one town and sell high in another. Played straight with most items, of course.
 * One town in Dragon Quest IV is short on armor for a while, and will buy armor for far more than it costs, at least until each type of armor is sold enough.
 * The merchant Taloon is also able to invert this for a time during his chapter after setting up his own shop: his wife will sell any goods you give her at a much higher price than any of the other shops around. Lady must make one hell of a sales pitch... Needless to say, this can be abused to Game Breaker status, if you know how to work the system...
 * Also averted somewhat in that the Casino charges different prices for gaming coins depending on what chapter you are in. The cash-strapped sisters of Monbaraba get discounted coins for only 10 gold each, whereas the aforementioned merchant has to pay 200 gold each. In the final chapter, the Hero's party pays 20 gold each.
 * Played straight in Xenosaga, in which all goods cost the same amount of money everywhere, and no goods ever increase in price. Acknowledged and possibly averted somewhat be a subplot that involves possible cuts in price depending on free-market investing on Shion's part. However, a shop is a shop is a shop in Xenosaga.
 * Which makes perfect sense, as their version of the internet, the UMN, includes a FTL teleportation system that can transmit non-living objects. Where you are really shouldn't budge the price, you can download it anywhere!
 * Inverted in the Tales (series), going all the way back to Tales of Phantasia. You can break the game's economy horribly by buying and selling stuff in bulk in the right towns.
 * The Elder Scrolls series is a rather egregious offender considering one of the big selling points is being a sandbox that allows for more playstyles than endless dungeon-crawling. But you're pretty much limited to alchemy and thievery, the latter of which isn't as lucrative as it sounds because nobody has anything of value in their houses. While it would make sense that items would be cheap in the big cities' trade districts and more expensive in little podunk shops with supply problems, prices are set by item so they remain basically the same, excepting some skill-based variation and how much the merchant likes you, no matter who's selling.
 * At least in Morrowind, if you have high mercantile skill and the merchant likes you, you can buy something and sell it back to the same vendor for profit.
 * Dragon Age Origins -- sale and purchase prices are identical wherever you go in the world (even though availability varies), and the only crafting item that makes a profit (i.e. the finished product can sell for more than the components cost) are high-tier Lyrium potions. One merchant in the entire game averts this, and only if you're a Dwarf Noble.
 * Chrono Trigger gets particularly insane. You would expect that prices would increase over time, the business with Lavos in 65,000,000 BC, 12,000 BC, and AD 1999 causing various economic crises, right? Right? Wrong. A Tonic is a Tonic is a Tonic, regardless of the time you're in. Even in 65,000,000 BC, when gold is a "shiny stone".
 * Averted in Secret of Evermore: In the same bazaar where you get the trading quest chain, there are loops that allow you to gain money (by buying cheap goods, trading those goods for more expensive goods and then selling the more expensive stuff to an appraiser).
 * Averted in Fable, where you can make money through arbitrage, or (thanks to a Good Bad Bug) sometimes even buy things in bulk and sell them back to the same shopkeeper at a profit.
 * Particularly bad in Geneforge: While the price to buy a good may vary from town to town, the price you get selling that good is the same everywhere, and it's less than the cheapest amount you'll pay to get that good.
 * Averted in Fallout 1 and 2. The price you sold things for was fixed (RadAway always sell for 500) but the buying price varied depending on your Barter skill, reputation, and the general disposition of the merchant in general. In several cases you could actually buy things for less than you sell them, allowing you to literally clean out the store by buying everything and selling back smaller and smaller shares until the merchant was left with a single chip or a worthless junk item.
 * Followed fairly straight with the regular merchants, but averted hard with the robot traders on Sender Station. (They're not trading in robots, they're actual robots who trade stuff.) They only trade various useless luxury items (and also lifepetals, but you need them for other things) but each have different price listings. Simply buy as much as possible of a ware where it's cheap, then hoof it over to the one who buys it for a high price. Then repeat, but now you can buy even more. If you can stand the repetitive clicking, you can make your party economically independent in less than thirty minutes. And you can always go back if you need more.
 * Averted in Saga Frontier for Gold Ingots, which will rise in price the more you buy and drop in price the more you sell; in fact, you can abuse it to make yourself obscenely rich.
 * Merchants in Albion may have varying prices. Some even have two separate inventories for selling and for buying that have different exchange rates, but the rule of thumb is that regardless of the exchange rate, they will give 20% less for everything you sell them, then what they would ask when you're buying the same item. The way it's set up, buying something from the cheapest merchant then reselling it to the most expensive merchant will most likely get you the price back, but not much more. On the other hand, there are a LOT of merchants who are more than willing to buy your hard earned loot and Vendor Trash, for pocket money (read, half the price an average merchant would give you).
 * In Final Fantasy games, items can generally be sold for half the purchase price. However, in Final Fantasy VIII, the player can learn the "Buy Low" and "Sell High" abilities of the Tonberry GF, which allow the player to buy and sell items at 3/4 the standard price. With those abilities and the Carbuncle GF's "Recov Med-RF" (Recovery Medicine Refinement), you can buy Tents and Cottages, turn them into Mega-Potions, and sell those for about a 20% profit.
 * In Guadia Quest of Retro Game Challenge, there are bars of precious metals that sell for the same price they cost. However, these are useful, as they prevent you from losing money if you are wiped out.
 * Unintentionally averted in Dark Chronicle. With the exception of gold bars (which buy and sell at the same price), the game plays this trope straight. Except that a certain golf club that sells for 230 gold can be made for only 90...

Mecha Game

 * Armored Core is this in spades. No matter how ravaged the land due to war is, that little missile launcher will still only cost you 12000 Coams all the time.

Simulation Game

 * Nook and Able stores in Animal Crossing series buy everything for one-fourth the selling price. In games with the periodic "Flea Market" event, NPC neighbors will pay about twice that. With the exception of white turnips and fruit, which are hard to take advantage of without multiple systems and multiple copies of the game, the price for everything is the same in every town. So the primary way to make money is to pull Vendor Trash off the trees or out of the river, and that's rate-limited by the system clock.
 * Aerobiz: Though you can sell old aircraft to "World Lease" at half-price, you can never purchase any used aircraft to bolster your fleet, and all aircraft are sold at a fixed price which never moves even as the design ages.

Tabletop Games

 * In Dungeons and Dragons, everyone uses the same currency and goods tend to cost the same everywhere. Pretty much an Acceptable Break From Reality given how much trouble having to exchange bits of your vast fortune everytime you left the country would be. Not to mention that sheer amount of head-scratching that goes into a spell that costs "20,000 gold pieces worth of diamonds" when the amount of actual diamond that is varies wildly depending on how you calculate it.
 * There still ends up being little holes in the game's default price lists that allow for capitalist enterprise (assuming the DM is a pushover.) For example, a ten-foot pole costs four times as much as a ten-foot ladder, so even if you can only sell items at half price, you can turn a profit by buying ladders, breaking them up into two poles each, and selling them.
 * Averting Cut Lex Luthor a Check with spells, a character could fill a warehouse with trade goods with Fabricate. Just hire near free unskilled laborers to collect the raw materials, spend a minute casting the spell, and then have a couple of skilled workers to handle the books and some guards. You'll make thousands. If you also know how to make masterwork weapons or alchemy, dropping masses of masterwork longbows or alchemical goods on the city could be even more hilarious. Offer to equip the king's archers for half cost. Since Karl Marx Hates Your Guts and you can only sell them at half price, you should sell them in no time flat. The spell costs 1/3 the value of the goods to create them and you are forced to sell for half, but remember - you can make 90 cubic feet of goods in a single casting at the minimum level. Or 9 cubic feet if you make minerals. That's about 4,400 pounds of steel goods. That's almost 9,000 masterwork daggers, if you are good enough to make them. Dozens of spells are ripe to be abused through these kinds of mechanisms and are not so absurd as cornering the ten foot pole market.
 * In 4th edition this gets even worse: you are not allowed to sell an item for more than 20% of its buying price. This is because enchanting magic items is much easier and cheaper in 4e than previous editions, but you're supposed to be exploring dungeons, not mass-producing +2 longswords.
 * This particular quirk might be explained if the adventurers always purchase magical items "on commission" - if there is low market liquidity, you might have to lower prices a great deal in order to move surplus stock quickly, and most items purchased will be made-to-order rather than off-the-shelf. (This may be giving too much credit to the game designers.)
 * The official Hand Wave for the low selling price is that trafficking in magic items is very risky and expensive -- it's hard to find buyers since adventurers are rare, and magic items are high-profile targets for bandits and thieves.
 * This leads directly to one of the worst aspects of the 4th edition: The official adventure paths are VERY stingy with giving out magic items to the players, only one in every couple of encounters. Every player needs at least three magic items (Weapon, Armor, Amulet) to be up to date to be competitive, so it hurts a lot more than in previous editions if you happen to find an item you cannot use. Like, finding a +3 Longbow when no one in your group is an archer. If you try to sell or disenchant the item you only get 20% of its value, which makes this highly ineffective, and you lose a valuable item without getting a proper compensation.
 * Magic items are intended to be rare and you aren't supposed to be required to have them at all. During third edition, a vicious circle developed between magic items being too easy and enemies being balanced to acknowledge how easy magic items were to get, which led to magic items being even more common for defeating those enemies causing even more powerful enemies with even more powerful magic items to emerge.
 * It also makes rust monsters, formerly one of the most frightening creatures to a fiscally conscious adventurer, into an extremely useful pet. In 4e, magic items can be disenchanted by a ritual that yields a powder containing about 20% of the magic essences needed to make the item. However, if a metallic magic item is fed to a rust monster, it leaves all the magic behind in powdered form.
 * Lampshaded in this Full Frontal Nerdity strip. "How does that make economic sense? You'd need state funded wizards cranking this stuff out!"

Wide Open Sandbox

 * Similarly semi-averted in the Escape Velocity series. While ship upgrades cost the same wherever they are available, trade goods are available for different prices on different planets, and random events can drive the prices further up or down. Certain routes are known to be such good money generators that cargo space itself will quickly become the limiting factor in how rapidly you can accumulate wealth (with a 50% margin between buying at "lower" and selling at "higher" it becomes a matter of finding an expensive enough good to fill your hold with for it to even be worth your time later on).
 * Completely averted in Elite, which is kinda the point of the game.
 * Played straight, however, if you try intra-system trade in Elite 2 or FFE. The prices on all planets of the same system are the same, unless some commodity is in dire need somewhere (but then again, most likely this commodity is unavailable on any planets of this system). The only ways you can make money without FTL travel are mining and waste disposal, and both have very low profits.

Action Adventure

 * Averted in Sub Culture, where some items are bought higher in some places than they are sold in others. Refined thorium notably is sold cheap by the refinery and can be resold for a good price in cities.