Since casinos always hold a great amount of cash, they have always been a target to be cheated on. Specially, traditional slot machines were considered a big chance for defrauders to make a lot of money out of them, since older slots operations were purely based on mechanical equipments, it was not so hard to come up with a cheating device or an idea to cheat them. However, newer slots and online slots which use micro chips and anti-cheating technologies are almost impossible to be defrauded. One of the historical and popular ways to cheat a mechanical slot machine was to use a wire to spin the coin into the slot machine, since it was a legitimate coin the credit would be granted by slots, however the spin caused by the wire in the slot machine made the coin to exit through the reject chute into the payout tray. This is an obsolete method of cheating slots, nowadays all large casinos replaced coin acceptors by bill acceptors and online slot casinos take credit cards or any other online banking schema.
In early 1990s still there were cases that people were successfully able to cheat casinos, one of the best examples is Ronald Dale Harris, he was a computer programmer working for Nevada Gaming Control Board and was responsible for finding flaws in computerized casino games. Harris took advantage of his knowledge and expertise to illegally modify certain types of slot machines, since he had access to the source code running on the core of these slot machines he made a few modifications to the software so that if certain sequence of coins were inserted into the slots they pay a large sums of money. Between 1993 and 1995 he accomplished one of the most successful and undetected scams in casino history by stealing thousands of dollars from Las Vegas casinos.
Another well known cheating device for newly computerized slots was called "slider" or "Monkey Paw" which was invented by Tommy Glenn Carmichael, this cheating device was a very simple piece of steel about 8, 9 inches and was bent on one end. By inserting this device into the payout chute, this device caused the coin counter of the slot machines malfunctions and as a result the slot overpaid the player. Modern slot machines use certain technologies and anti-counterfeiting devices to avoid any of these tricks.
Never try to cheat a casino or online casino; it is not worth getting caught!