I think the bottom line is in how you approach these problems.
I agree with previous poster. document, document, document. It's very difficult to argue with a well documented case.
I would copy the dealer, Mercedes reps as suggested, Better business bureau, and any other state agencies the dealer maybe registered with. Make your expectations, dissatisfaction and expectations for resoulution clear. That's the only way to hope to get any type of satisfaction.
And, on the other hand, I think we all need to do a little better job of expressing our appreciation for a job well done. Just as important as complaining about a poor job.
On more than one occassion I've searched out the Manager at say Wal Mart to express my appreciation for a job well done by a clerk, sales person etc.