I worked at a Game store in Orange County.
This occurred on the day of the 3DS launch. It was very busy at the time and the store was full of customers.
A mom came in to pick up a 3DS system and 2 games. She brought with her a trade that added up to $100 exactly.
I ring her up, all is well, and then I give her the total. ($250~ after the trade credit is deducted.)
She swipes her card, inputs her pin, I hand her the receipt, and then she stops.
Woman: "You stole my hundred dollars!"
All I could do was stare at her, mystified.
Woman: "You did! You stole my hundred dollars!"
I asked her to explain how that could be so.
She then argued that I overcharged her a hundred dollars so that I could personally pocket her hundred dollars in TRADE IN CREDIT, or else somehow turn her debit transaction into cash and whisk it away to my pocket.
I took her receipt and tried to calmly walk her through how the totals add up:250 for the system, about 30 in tax, one game was $40, the other was $30 = 350 -100 etc.
Woman: "You are a thief! You are stealing from customers we should call the police."
So I calmly walked her through it, again, with a calculator and a pen and paper.
This only made her more angry, and she started really screaming about it, at which point my manager came over and asked if he could help. I put my hand up, told him I had this under control, and recounted it for her again. Slowly. Loud enough that all of the customers could hear.
Me: "Ma'am, what was the price of the system?"
Woman: "$250 but-"
Me: "And how much were the games?"
Woman: "About $70 but that-"
Me: "Ma'am, are you aware of Sales Tax?"
Woman: "Yes but-"
Me: "Sales tax is on the bottom of your receipt. It's a bit over $30."
Woman: "But my credit."
Me: "Ma'am, if you add those numbers up, $250, plus 30, plus 70, you get $350. Do you disagree?"
Woman: "Look, you're -"
Me: "You had a trade credit of $100. If you subtract 100 from 350, is the answer 250?"
She didn't answer, so I continued.
Me: "How much did you pay?"
She still didn't answer, so I read it aloud off her receipt. One customer in the line for the other register started chuckling at this point, which really helped me punctuate how wrong she was.
At this point she snatched her receipt and items and left the store, embarrassed, still grumbling about how I'm a thief and that this still doesn't seem right.
The lesson is, don't accuse people of theft when the only thing that's gone missing is your own common sense.