I did CompUSA repair work in the late 90's - in fact it was my first tech job so in some respects I'm grateful for it and in others I'm not - This was back in the day when top of the line HD's were 8.4 gigs and memory was sold behind the counter
We always ran an above the board shop but let's face it - that goes from manager to manager - a lot of our guys (myself included) were just young people though we had an antique or two around to fix Apples and Printers -
some of the issues we saw were Operating issues - this got to be a major headache - format/reinstall is what we eventually ended up doing across the board - we can't fix OS problems like that
Viruses were horrible but at the time, most were bootable from floppy and most boot floppies cleaned them out - those were the good ol' days
we would occasionally get some folks wanting to upgrade and we'd often point them to the refurbished computers because to upgrade a 486 to a top of the line pentium would after install fees, cost less then buying a new pc - (kinda still holds true today actually)
we'd have people wanting free advice, drivers, help - we'd do what we could but at the end of the day you can only do so much over the phone - so much of the work was diagnostic/detective work with no easy 1 spot fix...
and we had some fun stories - like the PC that came in for repair with the gay porn desktop wallpaper - which then showed out thru the window of the shop into the main store for a couple minutes before he came back to the pc - and the wife who returned a PC in the AM only to have the husband want the same PC back (with no data lost) that evening - (yep, full of porn, which in dial up days took time to acquire)
my favorite is a virus infected and OS damaged custom built beast our master tech worked on for two days - two weeks later the guy came back complaining of the same issues - we asked if he had done anything to the pc and he pointed out that to get his data back, he restored from the tape backup he made 3 weeks ago - DOH!
I could see where mom and pop shops in the strip malls might be angling for a quick buck, but never saw horror stories like that at my shop