Their service work is poor and their customer relationship skills are horrible. Here are some examples:
Took my 2006 ML350 in (still under warranty), for a chirp in the engine. They had it all day, said they fixed it, before I pull out of the garage, chirp starts again. Took them 2 more tries to get it fixed.
Next time, I went in for a service B and had a headlight out. I pull out of the garage and headlight goes out, I asked if they changed it and they replied, oh we jiggled it and it came back on. It is a Mercedes, I can pop for a new light bulb.
ML350 was in for a detail and had a bad seatbelt. During the detail, they removed the bad seatbelt and ordered a new one. The good seatbelt was accidentally placed under one of the seats in such a way that it looked like it had been removed not just by me, but by their service adviser. The service adviser asked a mechanic where it went to which he replied that I must have taken it out! Me the guy that came in to get a light bulb changed.
I had the reservoir on my power steering go out. I paid for new part and they would call when it came in. 2 weeks later, I called them since I had not heard from the, and they responded, we installed that already. Are you kidding me, I think I would have noticed me going to get my car serviced!
I have several more, but the worst was the last one. My engine started backfiring, with 65, 466 miles on it. Took it in on a Wednesday expected a call say by Friday with a clue as to what was wrong, nothing, no call. I called them and they said tomorrow they would have more. This went on for 30 days!! I got to a point where I only called once every 5-7 days or so, but never once did they call me. I called Mercedes of Westmont, IL (150 miles away) to speak with an adviser to just get advice and the guy was even willing to act as a middle man dealing with my current dealership. of course the service adviser at Suds Mercedes in Normal literally flipped and refused to speak with me at the very notion. Mercedes of Westmont was providing the service I expected even though they had nothing but reputation of being a Mercedes dealer at stake. No money, just the Mercedes name. I called MB USA and complained and finally got a call back apologizing and got some information on next steps, but then no communication. Even after the problem was diagnosed, did I get a call? Nope.
In the end, it still cost me $$ for the repair (although MB USA was good enough to pay some of the cost), but I had no vehicle for 30 days and they offer no loaners.