I wonder if a repair shop would consider buying their parts from the vendor
of YOUR choice.  That way, you can work out any concerns about warranty,
price mark up, and the like prior to the start of work.

I did this with a independent mechanic in the Albany, NY area who was very
receptive to the idea.  He started to buy a lot of his parts from a vendor
I suggested, was able to get more profit from these parts from his other
customers, and gave me a discount on both labour and parts because he was
more profitable in the long run.  No warranty fuss either.

Hey, it can't hurt to ask.  If you can prove increased profitability I'm
sure they'll listen.

My $0.02 worth.

Alan Bosch
"...fah'n, fah'n, fah'n, auf der autobahn..."