There have been countless threads on AB where people have said that they've lost important files after PC World have reinstalled Windows. It seems to be their 'catch all' approach to fixing computer problems. On several occasions people have described the symptoms they were experiencing before they took their computer to PC World and I've strongly suspected that, had they asked here first, I could have told them how to fix the problem for free in only a minute or two, without any need to reinstall Windows. I'd NEVER use PC World!
I also dislike their 'flat fee' way of working. For example (unless it's gone up since I last looked) they charge a standard fee of £50 (plus parts, where relevant) to fix any problem on a laptop. Given that most of the things they'll be doing (such as removing malware or resetting the TCP/IP stack) will take no more than 5 minutes at the very most (and often only a minute or two), that's at least£600 per hour for many tasks!
Although I answer plenty of questions here in 'Technology', I'm definitely not an 'expert' (and probably more of a 'bumbling amateur' really). What worries me about most of the 'experts' at PC World is that I seem to know vastly more than most of them do about how to do their job!