Mercedes Benz's service is the worst there is in every city, not just Austin. It's because of that that most of my family has switched to lexus instead.
You are guaranteed a lexus whenever you take it into the shop for maintainence(which is almost never) and you can bring your car in at any time for a free carwash. The people are friendly and receptive, so you don't feel like your being screwed every time you take your car in.