I know for a fact this has happened to me at least once. I had a meal at Mexicali Concina Cantina in Studio City, CA. I paid with a credit card and left a cash tip. When I got my credit card statement, I happened to have the receipt handy, and I discovered that I had been overcharged by exactly ten dollars. I called my credit card company, and they reversed the charge.
Punny Money has a way to help you catch tip fraud without having to compare your receipts to your statements (you do need to save your receipts, though). You use a checksum method. Adjust the pennies in your tip so the last digit to the right of the decimal point equals the sum of the digits to the left of the decimal point of the total bill.
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. Come and hear Mark speak at the ALA conference in Chicago on July 1.