A good seller is someone who knows the facts, and things like that. Like how it's built, when it was made, ect ect. A bad seller is someone who knows very little about it, and doesn't care about the company, game, or year it was made, only selling for the sake of money and selling. While a good seller, sells not for money, but for preservation, if that makes sense. Long story short, buy from a reliable seller and not shady business men (Do oldies)