Getting fed up...

Don't get me wrong, most of the stores around here have at least a couple of knowledgeable people and try to be accommodating- especially to some of my more bizarre requests. But the quality/accuracy of some of the parts they get even baffle them sometimes. When I pick up parts now I always try to take the old one with me, and a pair of dial calipers. If it ain't right, it don't leave the store.
Electricals are the big pain, since many places will not (officially) accept returns on electrical parts. One time with a voltage regulator, I told them if they didn't take it back, I had the rest of my (rather large) order in the back of the truck and I would return ALL OF IT. The manager looked at me and grabbed it off the counter and threw it in the trash and credited my account.