All the Final Fantasy games that weren't ported to the console seem to be excessively sensitive to any form of scratching or scuffing to the CD. I originally got used copies of Final Fantasies VIII and IX and, although the scuffing was very light, neither would play properly. Getting new copies fixed this. I can't say for Final Fantasy VII myself, as I started off with a new copy, but I've seen a few reports from people with only light damage to their CDs - and the game won't run, or has problems.
Some other games I've had with far more severe scuffing have played fine. I don't know why the Final Fantasy series should be so affected in this way, but it would seem they are.
