The quality does vary... I've used them for several years now but only been unhappy on one count.
I always ask the guy: 1. How many years have you been in the game? 2. Where did you work before? 3. Talk about the process of the repair (and I can tell if they are making isht up or don't sound confident in their abilities... I'm good like that, reading between the lines... may be its my psychologist job haha).