Maybe I'm getting cynical with age, but ....

I know exactly what you mean. I used to do side jobs and stopped because these people (mostly women) would come back and say "well....all I know is, the radio stopped working right after you adjusted the valves" LOL That's super-stressful, because you're running an honest place and doing the right thing and you get accused like that. It's a slap in the face, and they don't know jack!!!

This is why I got into working on buses for the city transit system. Plenty of room to work, and no rush. Got electrical gremlins? Need a whole day or maybe 2 to troubleshoot? No problem. The bosses may get a bit grumbly but as long as they feel you're not just playing games, it's no problem.

Well, you yourself said it......you've got plenty of good customers, so why not put this lady on your "sh** list" and give her astronomical estimates for any work she comes in for? But I would NOT do that fuel pump for nothing!!