I've used the local (MK) Dent Devils guy a few times over the years, and the results have always been perfect, the trouble is that despite the training and the tools the results will only be as good as the bloke using them. In your position, I would talk to a local Mercedes/BM/Jag etc dealership and ask who they use (which is what I did some years back and they all gave me the same guys numbers)
Good luck.
Stu.