Coin on a String Trick

Characters inserting a tied coin into a coin-operated device and then pulling the coin out with the string to get a free item or service from the machine. However, this trope also extends toward other things.

Later in the 1980s, when video game arcade operators realized that people were doing this, manufacturers started putting a string cutter into the coin mechanism. If you tugged back to try to hit the switch again, the string would cross the cutter and be severed by it, thus capturing the coin and preventing its reuse by the crooked customer.

Not to be confused with Heads-Tails-Edge, when a coin flip is tied.

Film

 * Yellowbeard: Commander Clement wants to get some information out of Harvey "Blind" Pew but doesn't want to pay for it. Each time he drops a coin into Pew's cup, he yanks it back out again with a string.
 * Treasure of Swamp Castle: The guard is a victim of this trope used as bribery. Though it's done without string, two characters invoke this.

Literature

 * In The Black Spider-Knight Leopold XVII, to take a chance at slaying a dragon the eponymous knight needs to go through an automatic toll booth first, and the fee is a pocket of gold coins. Jamming a sword in the money slot doesn't help because it has apparently been built to withstand this kind of abuse from this setting's knights, so Leopold XVII tries this trick. The string is immediately cut by built-in automatic scissors.

Live Action TV

 * Red Dwarf: Rimmer tries this once, only to discover that the (sentient) vending machine is keen to this trick and equipped with an alarm.

Newspaper Comics

 * This Garfield strip made use of this trick with a cookie, instead of a coin.

Video Games

 * The Escape the Phone Booth flash game
 * In Zork: The Undiscovered Underground, the protagonist has to use this trick to get the information they need out of a coin-operated Creator Cameo. It Only Works Once, though.

Western Animation

 * Done in the 1937 short Magic on Broadway. This was part of Paramount/Fleischer Novelty-Cartoon shorts which featured animation in part of it and live-action in the other half. The cartoon half of this entry has a slot-machine player cheating the machines in a penny-arcade by tying a string to the coin and pulling it out again. The machines get rather animated about being cheated and the petty-gambler receives some rough treatment.
 * Bender from Futurama is fond of the coin-on-a-string trick. The first time he uses it is in a suicide booth (What is he saving the coin for then?)
 * In "The Duh-Vinci Code" he tries it with a giant coin. It tears his arm off.
 * SpongeBob SquarePants: Mr. Krabs uses the coin on a string on occasion, as in one flashback.
 * Donald Duck's early films has him using this technique (a la Mr. Krabs) to economize at a fair.
 * Top Cat does the coin on a string trick during the opening credits; snatching the coin back from a doorman after he has tipped him.
 * In the Warner Bros. cartoon short The Mouse that Jack Built, the mouse played by Jack Benny goes down to the cheese vault (counterpart to the money vault in the radio shows). He opens the first door by putting a coin on a string into a box, then pulling it up again. Since Jack Benny often played a cheapskate in his radio shows, this might have been to keep in character.
 * A flashback on The Simpsons implies this helped Mr. Burns make his fortune.