I agree with Steve, too.
My independent mechanic has solved problems on my car, and replaced components in the process that probably in the end didn't fix the problem.
He has always said that he wouldn't charge me for things that didn't fix the problem, but I've always insisted in paying him for parts and labor.
He is a hard-working guy who owns his own shop, making an honest living, supporting a wife and two little kids. He's not wealthy, but is working hard to support his family.
I'd rather give him the benefit of the doubt. At times, he has done small things free of charge, knowing that I'm a reliable, repeat customer. He always recognizes my voice when I call by saying "How are you Mr. Smalley?". He knows I hate being called Mr. Smalley, preferring to be called, Paul, and he does this to tease me. It's a running joke.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".