I agree that most record grading is spurious and has no correlation to the sound. Many records are M or near mint. The latter should mean pristine, perhaps played once and unmarked, they very seldom are. Visual grading is useless anyway, you need to play both sides and what commercial seller has time. I agree with Arahl, get to know sellers you can trust and stick with them.
A good vacume clean does make a big difference too.
A good vacume clean does make a big difference too.