Who has told a buyer that what you have is not what they need?

I used to all the time.
When I was still working in a Mopar parts room, I'd have people come in with the interior lighting timer in their hands.
I would look at them and tell them if they can tell me what that relay is, and what it does, I'd sell them one.
None ever could. They just knew it gets hot, so it must be bad.
I started doing that after I sold a couple and the customer would try bringing back claiming it was bad too. Then I would have to listen to them ***** because I wouldn't take back an electrical part.
Other wise, I sold people what they asked for, sometimes it wasn't what they needed.
Now I do it with keys. I won't sell anyone a trunk key unless I see theirs first. I'm not going to get into the reasons why, just............Mopar.