Dealerships have LOTS of overhead to support. The building, inventory, employee expenses, etc add up quickly. That has to be paid for. Most dealerships make their nut from the Service Department, not from selling cars.
In dealerships, EVERYONE is on commission, or some kind of sales-based compensation. The more that gets sold, the more the people doing the selling make. Even the techs have incentive to suggest services that may not be immediately necessary. Brake pads for example. There's lots of pressure to up-sell. The dealership manager is pressuring the service manager, who's pressuring the service writers, who are pressuring the techs, then pressuring the service customer for additional sales volume. The higher the sales, the more these individuals are compensated so there is tremendous pressure to charge as much as possible. Generally, these commissions or sales-based salaries aren't used in independent shops, particularly one or two-man shops. And, the indi shops don't have the tremendous overhead to support.
Like anything, the most important aspect toward purchasing services is being comfortable working with an individual that knows what he's doing. I have yacht clients I've worked with for 30+ years. And I have certain parts and supply outlets with people that I've know the same amount of time I get my materials from. These are personal relationships. Generally, these personal relationships won't develop with dealership personnel. There's too much pressure and internal back-stabbing going on because of the commission structure, so people don't stick around long.
I'm an example: I worked at a dealership in the 70's for 6 years. I began by washing cars on the lot, and after 2 years was on the line as a mechanic with 35 other guys at 100% commission. I found my niche, I was really good at what I did (I had no comebacks, my diagnostics and work ethic was exemplary, I knew how to fix cars) and I made a lot of money. But after 4 years of it, I was burned out and moved to a different deal. That evolved in to the single-man self-employed yacht gig I've been doing for 39 years since.
When I gave my notice, the dealership General Manager and owner came out and took me to his office. He was concerned that I was leaving. (I was always one of the top-3 producers of the 35 guys in the shop. He was loosing one of his top-three money-makers). I told him I was tired of being part of a team where 5 of us could fix cars, and the other 30 butchered them up to the point the customer was NOT going to be returning to us. How did these butchers benefit me? He admitted I had a point. Plus the cars themselves were pieces of ****, and had inherent problems. These were the first Volkswagen water-cooled. My niche was the Rabbit Diesel which came out in 76. I was the only guy in the shop that could time one, so I got all the cyl head and engine burn-ups. About 3-5 a week. As I said, I made a lot of money, but it was tough going.
There's some insight into dealership operations. I was there decades ago. Not much has changed.