A coworker had problems with his Mercedes SUV, opposite end of the spectrum from a used Sunfire. He had it checked out and came back to the office in a very sour mood. I asked to look at the quote - they planned to replace the plugs, wires, and coils (V8) for $3,600! I looked at it closer and saw a very common game being played. They used the numbers "from the book" for the hours required for each replaced component as if you would replace each component individually and added them all up. In reality, if you're replacing the plugs, you're already pulling the wires, so it adds no time to the work at all (maybe a few seconds per wire). There's not much to add for the coils if you're replacing the wires either.
After much prodding, I managed to get him to get a quote at a non-dealer shop and when he showed the guy his quote, he pointed out the exact same cons that I did. End result, he saved 2/3 of the dealer's quote.
I could tell you other (bait & switch, rudeness, etc.) stories about BMW and Audi dealers, including a coworker's experience trying to buy a brand new one.