Just a quick disclaimer, these guys are expensive. If you bought a Mercedes expecting the service to be cheap, you probably bought the wrong kind of car. I have bought all of my cars in Arizona from this company (one in Scottsdale, one at Bell Road). I have been treated very well by the sales staff and by the service staff. I cannot say enough good about Ron Moran (Scottsdale sales) and Phil Tiemeier (Arrowhead service). They take exceptional care of me and are very upfront and honest about what is going on with my car.
By the way, people who are complaining about paying for repairs and service, A) read your owner's manual about what is needed at each service interval, (B) if you didn't want to pay a lot for services, you should have bought the prepaid service plan, (C) if you didn't want to pay for expensive repairs, you should have bought warranty coverage. At some point, you have to own the car. This isn't Mercedes' car once you buy it. You own it, along with its problems. That was the choice you made.