Went to my dealer for a tire rotation and to get mud flaps installed on my
02 Impala LS. When I picked the car up, they had changed the oil without my O.K. Normally it wouldn't have been a big deal except they drained out my Mobil 1 and put in whatever stuff they use. Since the M1 had a couple K on it I didn't make a huge deal about that, but I did let them know I wasn't pleased that they performed work without a written or verbal OK.The good news is that they took the charge off my bill. The bad news, and the reason I change the oil myself, is that they overfilled it - about 1/4" above the fill mark on the stick. Everything I've ever read indicates that this is a bad thing to do, so I drained about 1/2 quart out the next morning. The other funny thing about this dealership is that they call you a couple of days later to make sure that you will only give them praise on the survey from GM. If you're anything less than 100% pleased you don't get a survey!
The other good news is that the tire lugs we're actually pretty close to being torqued right, unlike my Dodge dealer, where some lugs are so tight it takes all of my strength/weight (6'3" and around 240) to get them off and others where you can almost spin them off by hand.
The point of this rambling is that if you can't trust the dealers (who supposedly know these machines better than anyone) to so simple things like rotate tired and change oil correctly, how can you trust them on the big stuff? How many "average" car owners even bother (or know how) to double-check the shop's work?