Sparky,
When I was in business and found problems on the job, I would list them on my bill. For example, I would put a note on the bottom of my bill, that we found such and such wrong, which is in violation of the NEC. I would also make note that it should be corrected. This way if something did go wrong, I could prove that I notified the customer of the violation. My accountant and I figure that if the customer took the time to read my bill, then they would have seen my notice of the violation. Who knows if it paid off?
Harold