Yep, better to lose a bit and learn your lesson then do something you're not proud of and send it out. I don't let the customer bring his own parts. If he does, I had a form they had to read and sign before I did the work. Pissed some people off, but I got tired of working for free.
As I got older, I just told them to take their junk somewhere else and I had a little sheet of paper with all the other local machine shops phone numbers and addresses. Gave them the options.
