A friend I sent this to emailed me an experience of hers:

"How about this one:
Several years ago, at a bottle return depot, I was given substantially more
refund than I was expecting. When I pointed this out, I was answered with a
string of verbal abuse for questioning the amount. While delivering this
tirade, he recalculated the amount, and finding his mistake, thrust the correct
amount of money at me and shouted "see, now you get even less money".
Needless to say, I left there shaking my head."