Any person operating or working in a shop runs into people like that all of the time and it’s extremely frustrating. About all you can do is try to cover your tail end as best as possible because when it comes to people and their cars the sky is the limit on lying or just being utterly ridiculous about the situation.
It’s too bad that someone doesn’t compile a book (a very thick one obviously) of shop war stories. I’m sure tragedy, comedy, anger, and downright amazement would be well covered. My feeling is that it would be a top seller amongst automotive service people. 