My friend used to work with me at the service desk/video department.
Whenever someone had "late fees" on their video rentals, he would tell the person about it.
If they said, "Oh, okay." And started to pay for the late fee, he would tell them nevermind don't worry about it and delete the late fee from the computer.
If they said, "No! I turned that in! Blah-blah-blah!!!" He would make them pay for it or else tell them they couldn't have a new rental. They would get soooo PISSED, and he would be happy.
I do stuff like that now.
One time I was getting ready to leave (about 5 minutes later than I was supposed to), and this old guy says, "SO! You're gonna just close when it's this busy???"
I said, "Yep!"
He said, "Well then, I'll tell ya what! I'll just shop at Safeway!" He then sets his basket of groceries down on my checkstand.
And I say, "Okay, have a good day." And leave.