[HarryD]

My feelings are known. If I do bring the parts to my wrench (as I have when I was unable to complete the install), it is clear that there is no warranty but the labor charge is the same. I usually tell the wrench to add a bit fto cover his lost profit. Most of them have been kind enough to not add a "corkage" fee since they are decling to warranty the work.

It comes down to your relationship.

Also, with the shops I deal with, I will occasionally ask for a bit of help on a DIY to keep me from doing something stupid (think of JW's advice here). I feel this is part of the relationship as well.