I also prepaid for service, and I'm glad I did. Huge savings. Also, they offered a loaner, but I didn't need one, so alternatively, they offered to pick the car up from my house and return it. The best thing though is that I wanted to switch out my summer tires for winter tires, but my car is an AMG with staggered wheels for which MB doesn't offer a winter tire set up. The guys searched other vendors until they found a staggered set in the OEM specs. By the way, I also checked with other vendors and they all wanted to sell me front and rears in the same size.
I've dealt with this dealership for over 10 years now and have witnessed a complete transformation in their approach to service. The guys are great and the service they provide is impeccable, and this is coming from a customer who had a five figure repair bill on my previous car.