Today I went through my bank's drive thru. I pulled up about a car length and counted my money. I circled around and gave back ten dollars which they had over-paid. I checked my slip and saw it had the amount I had asked for. She thanked me profusely. I told her I would have told her if I'd been shorted so it was only fair to tell her when overpaid. A mistake can go either way so it is important to check even though they usually get it right.
I also check to see if my prescription is actually mine. I've gotten home before with somebody's heart medication. I had to drive back (20 minutes) and get mine. I gave them back the other prescription, but I don't think they used it. It's easier to check before driving away. It doesn't happen often, but it does happen.