It all depends, I tend to get games, and get them up and running pretty quick. Those will tend to have problems, as I haven't spent any real time on them.
Games like my Pacman(s) or any game where I have restored it, everything get's a through going over, forums read for common problems, and those areas paid special attention too. Those are the games that once done, I have no problems with. Which means I'm up to 7 solid games out of 14 atm. But my Galaga is almost done, and I think Tempest will be the next in line.
My Tempest that is tempermental, needs a new interconnect, and an Asteroids that still has a strange monitor problem, and some sound issues on my BZ. I tend to look at those problems when I get a chance, but once I re-furb, or restore them I should have no major issues.
I find taking the time to go over the areas of common problems, helps tremendiously.