I don't really like the idea for one reason. The only result will be a sharp increase in price gouging on Ebay. It's bad enough you have every other video game auction with the word "RARE!" posted everywhere. All this will do is drive people to put "GRADE A!" everywhere too.
Let's face it. Most people are smart enough to tell if a game is beaten up or in good enough condition and will negotiate based on that if they really care. A formal grading system will, like baseball cards, cause the value of ungraded games (regardless of quality) to drop.
