I took my BMW to Autotech with a check engine light on. They diagnosed the problem and gave me an estimate of about $900. When I picked up my car, the bill as actually $1200 as they made an independent decision to do some other things to the car, one of which was to replace the filter for the ventilation system. Really?
I later noticed that they had replaced the gasoline cap. While the many things Autotech fix may have all been good things, I suspect that replacing the gas cap alone would have sufficed.
After all the upgrades -- tune-up, new software update, yada yada yada, the car now gets on average .6 to .75 fewer miles per gallon.
I was told that for another $1000 "the car will be like new, and will run with nothing except oil change for 120K miles.