I work in a dealer (not mercedes I must add) and it really is true that making customers as happy as you were made today is key these days. I'm sure you'll tell people, you already have, and probably go back there too.
People make any business, but when it comes to retaining customers, it is the only way to survive.
Great news that they looked after you so well! A real result getting your car MOT'd for another year, always a good feeling to get that sorted.