When I was a privateer racer, I used an engine builder. Now, I was a very good customer, and spent about $6-8K a year with this fellow. Well, he didn't carry some specialty parts that I wanted to use, so he saw no problem with installing them for me.
In this case, we had a long term relationship, and a good understanding. He had confidence that I would choose the right stuff, and knew I wouldn't grind him to death on the labor.
But, someone just calling out of the phone book would not have been afforded the same treatment.
It goes back to my example of some customers spending hours of time trying to save $5. No business wants to deal with them, and it deathly afraid of letting them waste your time.
Steve's point is that a shop was just called out of the blue, and someone asked about installing parts they haven't seen.
See my post:
Did my Mechanic try to Rob me?
That'll give you a good idea of developing a good relationship with your shop.