Brent,
You did the right thing. When I was in business, I came to realize sometimes the best job is the one you DON"T get!
Imagine if this guy had you do the work, then through his own stupidity (forgot to fill his
oil, over revved the engine, etc....) blew up the engine right after you had rebuilt it for him with the right parts to make it run like he thought it always should have. No matter how much you tried to make it right, this guy would be trashing your reputaion with every other racer he could talk to.
Take the high road and realize there are just going to be days like that no matter what you do. I hope you were at least able to get something for your diagnostic time and trouble.
Bob