Ok, so I think I might use the grading coupons to attempt to sell some of my O'neal and MJ cards. I've been looking for prices for what stuff sells for..but I'm very very confused..many times nicer cards graded higher go for lower then a lower grade of another company. What gives?

Looking for TtA 57 in 9.0 or better, ASM 28 9.2, STT 101 8.0, and Cap America 119 9.6