I had that happen - a clerk kept giving me change for a hundred and she was supposed to take a roll of stamps off of the $100.00, she already gave me the stamps, I tried to explain to her she was giving me too much, she told me no she hadn't and tried to give me another $20.00 bill. I took the stamps out and showed them to her, she still didn't understand. So I laid everything on the counter and took my $100.00 bill. I then asked her to give me 5 $20.00 bills, which she did. Then I asked to purchase a roll of stamps, I think they were $42.00 at the time. I then gave 3 $20.00 bills and asked for my change, she gave it to me - then I pointed to the excess money and she turned white as a ghost, and just kept thanking me. I guess she was having a bad day. I used to be a clerk, my conscience wouldn't let me take the extra money.