my wife is also disabled so friends do our shopping. after a big grocery list (over $250) we noticed a $20 "cash back" entry on the register tape. we called the store manager (walmart, incidentally) and told him that we had not requested nor received cash back. since the cashier's id was on the tape, along with the transaction time, he promised to investigate. within an hour, he called back saying we had a credit of $20 at the store. mysteriously, that cashier was never seen again. presumably, ours was not her first compliant.

like any other alert or warning, if you choose to ignore it, don't kill the messenger, you're on your own, jack!