They say they can boost my c63s to 710hp and 1072nm.tq, anyone heard of them? Can they be trusted? Will it hurt my car? Any inputs are appreciated!

There are a ton of tuners out there claiming these numbers. I would be weary of most of them. Alot of these websites are copy and paste. i found one site of a well known tuner(for other models) that said 150HP and 175TQ with program switching. After some emails back and forth found out none was true.
Honestly I am thinking you should stick with one of the big guys for your 80k car. i am going to be doing more research on all the tunes and see what gets released over the winter

I think those numbers seem a bit ridiculous just for a tune...

Definitely OTT if it's a software tune only !!!

Look at the many tunes out there ATM from reputable tuners and all of them are around the same ballpark with software upgrade only.

Those numbers above would be realistic if it was a turbos and other components upgrade as well.

Alright, wont be doing it, thanks for the input!

and while we are at this, which companies are reputable? Can recommend some names?

Eurocharged, Weistec, Renntech are the 3 major players.
weistec offers quite a bit of additional parts to back up the tunes as well. they even have upgraded turbos. they have been in the game for a long time and have some insane builds.(like a TT v12 m275 in a c63 Black series)

Are these claims crank or wheel horsepower? PP-Performance is currently putting out the highest figures that I know of.