Although there are numerous versions used by suspects in raising the amount of change they receive, the following is the most common. It is known as the "short count."
Step #1: Con man buys a low-priced item, usually something for under one-dollar. He gives the cashier a ten-dollar bill.
Step #2: When the cashier hands back the change, the con says, “I really didn’t want all this change, and I’m sure you could use it more than I could.” He then offers the cashier ten one-dollar bills in exchange for the a ten-dollar bill he used to make his original purchase.
Step #3:The con must now get the cashier to hand over the store’s ten-dollar bill. This can be accomplished by holding onto the money until the clerk offers the ten-dollar bill. The con must now take the ten-dollar bill while simultaneously handing over the expected exchange money. What the con will actually hand the cashier is nine one-dollar bills and a ten-dollar bill, for a total of $19.00. (At this point, the clerk holds ten dollars that belongs to the store and nine of the con man’s dollars.)
Step #4:When the cashier notices that the customer (con artist) made a mistake, the con man acts surprised and thanks her for catching the error. If she fails to catch the intentional blooper, the con brings it to the cashier’s attention saying that he might have made a mistake and would she please recount the money.
Once the cashier is aware that she is now holding $19 instead of $10.00, the con immediately says, “Here, I’ll add another dollar to the $19 I gave you in exchange for a twenty. The con hands the clerk a dollar and takes the twenty. He then leaves the store with a ten dollar profit. (Remember, ten of the dollars in the cashier’s hand belonged to the store, so what the con actually did was to give her ten-dollars for a twenty.)
What the scam artists do in this particular con is gracefully mislead the cashiers by simultaneously carrying out several activities. In the present case, he made a small purchase, asked for change, made an intentional mistake, corrected it, and while making small talk cheated the store out of ten-dollars.
Beating such con artists is very easy. All you have to do is CONDUCT ONE TRANSACTION AT A TIME. In other words, finish making chance, and if the customer asks for more chance, treat it as a separate transaction. Do this and you can't lose.