A grading system has been analyzed to death. Too subjective for everyone to agree on. And it certainly couldn’t be used as a good reference for pricing. Two separate things. It’s a factor but condition sometimes is the last thing that affects value. It seems popularity/demand/ availability and then theme/value of fun set the bar and then condition may come into play. Prices fluctuate so much. Everyone kind of has there own grading system and price point for a game. I am sure we judge similar things but we put a different value on them.