I have serviced cars at Sullivan Parkhill for decades. Nobody there has ever recommended un-necessary service. The charges have been reasonable, and I have never had any problems with the work that was done. In fact, I have been told once or twice that I did NOT need preventive maintenance that I asked about. Honestly, how many dealerships will do that for you? They get me in quickly, shuttle me home if I don't want to wait. The Suburban comes out clean every time.
Sullivan Parkhill does my mechanical work only, I have no experience with their body shop. (For body work I have always gone to Tatman's).
I recently spent a lot of time working with Gary Longfellow in sales. He is very knowledgeable about many makes, not just the ones that he sells. Gary quickly figured out what I wanted from my mew car, and didn't put any pressure on me.
I highly recommend Sullivan Parkhill, and particularly Gary in sales.