So yesterday I had my electrician come to wire a remote controller unit into my ceiling fan. One of the pull-chains had broken, thus prompting the request. After he was done installing it, he said that the unit was a dud; it controlled the light correctly, but was not getting the fan blades to spin (even though we could hear a buzz from the motor). He checked his wiring again -- he has installed many of these so it was a pretty simple job for him -- and confirmed that there must be something wrong with the unit.
When I brought the unit back to the store, they were skeptical that it was broken. Since I live nearby, they asked if I could leave the unit in the store to be checked out the next day (it was late).
They called me back today to tell me that they had the unit hooked up to one of their fans and it was working. So I went back to the store with my fan (sans blades). After a quick hook-up, everything worked fine.
My electrician was puzzled, and so was I. He clearly knew how to hook these up (he has done lots of work for me). He came back to my house, wired it again, and now it worked. Obviously, he had made some sort of stupid mistake yesterday.
He was so sorry for making me run back and forth to the store that he refused to charge me anything for his work.
We all make mistakes some time, and clearly he had yesterday. I was more than willing to pay him something, since he came back and corrected his mistake. But he was upset at himself for not getting it right the first time, and he apologized by refusing to give me a bill.