Seems to me that a sometimes DIYer really needs to have a shop that will let them bring in the parts now and then. Sometimes you don't make a decision on whether to do it yourself until you see the part and figure out how it all works. In my experience a lot of good honest shops will let a good customer bring in their own parts. That's my first question for a shop and won't use a shop that prohibits it. I think a good honest shop doesn't have a parts profit margin that is so great that they have to be all that concerned about it. Of all the functions that middlemen typically provide to earn a profit margin an auto repair shop is performing very little of them. If their profits margins are that exciting to them I'm a little suspicious.