They charged me £300 for a brake pad job on my Rover. Went into my usual place for MOT two months later and it failed on brakes - majorly! Half the bits hadn't been put back properly and the car could have failed at any moment. Thing was, that far down the line, there was no way we could prove what they had (or rather, hadn't) done. The MOT place did say that there was no way the damage could have been caused by normal wear and tear in the twelve months since they'd last seen it. Even towing the caravan with it wouldn't have done that much damage, he said.
Needless to say I won't touch them now.
My son swears by this scheme:
http://www.goodgaragescheme.co.uk/ . I've yet to try it, but he's found a very good garage where he lives.