Many jurisdictions require a service business to give written estimates. Cehck your local laws.
I find that dealers seem to bundle everything into one big charge. They are famous for finding lots of things wrong, and only talk about the complaint at the end.
As I noted in another post, check if there is a service consumer survey in your area. In the DC area, there are few dealers who rate up there with the best independent garages. One is a Chevy dealer, still family run. The grandson of the founder has a 1915 truck in his showroom. It seems that the guy cares.
I've never worked IN the auto business, but service seems to be a continuing problem. I wonder if new cars are so complex that the average tech really can't diagnose it. That could be a major part of the issue.