I may be way off base here but I think the reason for Steve's aversion to the bring-your-own-parts idea is because when it comes to diagnosing and fixing a MB vehicle, he is better than 99% of any other MB mechanic out there, and he knows it.
He is honest, (not saying that any other tech on this board is dishonest) he does not throw parts at problems, as any frequenter of this board certainly knows -- he diagnoses the problem from his extensive experience and through smart, logical thinking. He does the job right the first time, and in this manner he saves customers big bucks.
If I lived in Tampa, my MB would go to him everytime I couldn't DIY. Here in Houston I have found a mechanic that will install customer-supplied parts -- he isn't the best mechanic around, but he's good for small jobs like a brake job that started this post, or other unsophisticated repairs.
Now, if my 300E develops a high idle problem that could be due to multiple sources beyond my expertise, I doubt I could trust this guy to diagnose it properly, in which case I would take it to a Stevebfl-type shop, which I have yet to find here in Houston.
Different strokes for different folks,
Have a great weekend all!
'91 300E, 212K miles