True story (from the U.S.): My mom's husband once went through the aisle at a Target (cheap department store) and bought a couple bags worth of stuff with a credit card. After the cashier rang him up, he waited in the aisle, looking puzzled, until the cashier asked him what was the matter. He said, "You never gave me my card back."
She: "Oh yes, I did."
He: "No you didn't. It's in your front breast pocket."
And without a word, she took it out and handed it back to him. Presumably her thought was that because he was elderly, he would assume he'd made a mistake. He wouldn't have time to double-check, though, until he made it back to his car with his hands full of shopping bags. That would give her more than enough time to copy down all his card information, and when he came back to say his card really was missing, she could pretend she had found it on the floor.