There are definitely good and bad dealer mechanics out there. I have two good stories.
We had the timing chains done in our old Traverse under warranty. The guy who did the work broke the huge plastic apron under the hood in half and put it back on in two pieces. and left the battery box open (its in the interior on those trucks, in front of the back seat)
I popped the hood when we got home to check for leaks (I do all my own work unless something is under warrantee) and drove it right back and showed the service manager. He apologized and ordered a new one for me.
Then it started getting a random knocking noise that would come and go. Took them months to find it. Turned out the guy left the tensioner bolt loose and it walked out...only thing stopping it from falling off and cause catastrophic engine failure was the fact that it hit the timing cover.
The dealer was very helpful in getting things resolved. He told me the guy who did the work was long gone because he had so many comebacks.
Second story...my FIL brought his miata in for an oil change, and they did everything but put new oil in it. Test drove it after, started making noise, so the tech brought it back and put oil in it.
Service manage told my FIL about it though and told him to let him know if there where any problems. Blew the engine on the way home and the dealer had to replace it. He asked them to do the clutch while it was part for the inconvenience and they refused.
I was amazed. Dealer cost on the parts isn't that high and the hard part of the labor was already done! They would have to pull the old clutch anyway to transfer it to the replacement motor, so not extra labour at all!
I would have been al over the chance to make a customer happy with $200 in parts and no extra labour, but I guess they didn't want to go any further in the hole after messing up a $40 oil change.
My best friend, however, is a great A tech. My father was too when he was still working. Fast, make great money flat rate, but low low comebacks. Can't make any money on flat rate fixing what you already fixed once!