Can't really vouch for their work but before I purchased my car it was serviced by Millenium Mercedes in Bedford which isn't a million miles away.
I phoned them up and the guy was very helpful going over exactly what work had been carried out to give me a good idea of the history of the car and deciphering assyst+ when he could have spent the time earning money instead. Even though it's a bit of a drive from me I looked up some reviews which seem good and may use them in future.
