Just make sure you keep your eye's open when dealing with them and don't get sucked in with the schmooze.
Like everywhere there are good and bad points.....the bad one I had, was when the poor old boy next to me purchased a 2010 C Class Coupe from them. Being a used car from Mercedes he didn't bother to check the car over. Anyway it came with 4 months MOT (can't believe they would sell a car with just 4 months MOT).
Took it to them for an MOT 4 months later and only 500 miles covered and the car failed on front lower ball joint, tyre below minimum and a sticking caliper which they expected him to pay for and then told him the car would need a service......total pi*s take. I him to take it up with the dealer principal which he was loathe to do as he didn't want any drama. So I went in on his behalf and after much shoulder shrugging they agreed to fix and replace the tyre for free.
Just double check all the paperwork and make that everything has been done, ie service, MOT etc.