Our theory is to only allow the dealer to service/repair our cars. That way, everything is on record at the delership where we got the cars. No warranties are voided due to the wrong parts, etc.
We've found that the dealers are quite good and take into consideration that costs you are facing.
The only people who touch our cars other than the dealer would be the tire place when we get new tires.
The dealers we continue to work succcessfully with are, Ewing Autohaus Mercedes (GREAT SERVICE), Huffines Chrylser in Plano (Jeep and van) timely service, fair pricing, and Town North Mazda (Miata) timely service, fair pricing.
The Mazda place could easily have increased our bill a couple months ago. I have a 2001 Miata hubby gave me for my bday in 2001. It only has 8800 miles on it because I rarely drive it. We do drive it in the Plano parade yearly. This year, we were in the parade as usual. When I took it out a couple of weeks ago to run it, the engine light came on. We took it in to Mazda and were told there was an automatic charge of $95 to look at it. We told them to go ahead with an oil change as well. Turns out...because I do not drive the car often, the gas cap was a little loose therefore it set off the alarm for the engine. Long story short.....it was a simple issue. Mazda charged us for the oil change and did not charge the $95 which they EASILY were allowed to do and we had agreed to.
I could go on with an issue regarding my Mercedes but the same situation as above is the end result. They always treat me fairly and with respect.
There are some good dealerships out there.
Good luck