Reeading this reminded me of something that happened here a few weeks ago, basically these guys we called to come clean the AC's of the house said it would cost a certain amount. Since it seemed quite like a low amount we went ahead and rounded it up to give them a tip which they were grateful for.

The funny thing is after a few more months we call the same guys again and either they remembered us or had just happened to increase the price, they quoted us for the amount we had rounded it up to when being generous last time.

Guess no tip needed anymore. :D