I never bought any used games for PS2 or PS3 but I did for PS1 because I was an apprentice only earning £66 per week (£1.67 per hour) so a full priced game was most of my weekly wage.
But the games I did buy were never scratched so bad they didn't work, one of the best games I bought used was Soul Blade, that game gave me hours of fun.
However I guess thesedays trying to find a perfect condition PS1 or PS2 game isnt going to be easy simply because some games will be over 10 years old.