Shops are run by people. You have the honest people and the dishonest sharks who give the repair industry a bad name. When I have run into a dishonest (IMO) shop then I take my business elsewhere. Upselling is common and not necessarily dishonest, perhaps overly zealous profit taking is a better discription. In general I expect upselling from new car dealers, chain stores, and corporate owned chains like Firestone, Goodyear, and Sears.
Upselling bothers me, so I use chains for basic stuff like tires. For real work I find a real mechanic with his own shop. Over the years I’ve been taken a couple of times, but far more often my system has provided me with good honest easy to deal with shops.
My current shop did a timing belt job on my son’s '00 Camry with 88K miles in '09. Last summer of '11 the car died on the road. At 120K miles the timing belt snapped. Fortunately it is a non interference engine. My son was 3 hours away on Long Island, NY. We got a AAA tow and used a AAA referred garage and the car was repaired quickly. LI rates are high, so it was $800 for a repair than should not have been needed. Turns out the water pump from the 88K job was faulty and went bad and took out the timing belt.
Back to my regular mechanic; he apologized and checked his records and the pump came from NAPA. We tryed to get NAPA to acknowledge the bad pump, but no luck. He checked the records for my other cars and water pumps were not from NAPA on those. This is a case of simple bad luck. My mechanic did the job properly at 88K miles and the 120K redo was done properly too. Car is home again this summer at 140K and in very good shape. I still use my mechanic because I have a history with him. Although this repair went bad, I don’t see he did anything wrong that would have avoided it. He does not use NAPA water pumps anymore.