Trusted garages are around and they are great. We have a spectacular one in Charlotte, NC that works on Hondas only unfortunately.
Otherwise, I've seen it both ways.
I was getting my car serviced by a small shop and was told I had a headlight out. So, I told him to go ahead and change it out. He could not figure out how to pull off the rubber seal on the back of the assembly. So, he just cut it off. I found out later when I saw moisture getting into my headlight. I've never seen boneheaded stuff like this from my dealer.
I own 3 Toyotas now. Dealer service has been spectacular. Plus the cars are so darn reliable, that they don't need much in the way of repairs. A friend was complaining about how expensive it was to change the oil on her Prius. A small shop was changing her oil every 5K. The dealer only changes it every 10K. So, just that alone would save her money. (Plus, the small shop was charging way too much).
I ended up buying my tires at the dealer as well. When they have their buy 3 get 1 sales the prices are reasonable. Now, it is not unusual for me to pick up the car and there is no charge for service. In those cases, the only real labor involved was rotating the tires and they rotate them for free if you bought them at the dealership.
You do have to watch them though. On a Honda minivan I recently had, the AC broke. They were going to have me replace a $500 computer and I figured out that the problem was a $29 part.
It is clear that people who don't understand car maintenance are at a huge disadvantage.