Unless you are forcing people to buy something or you are commiting fraud I don't see how morality comes into play here. If you can sell them at a higher price then more power to you.
Whoever buys your game obviouly values a rare game more than their $70 or whatever they are paying. You gain the money you wanted and they gain a rare game they wanted ... who is the loser in this situation?
Go for it and sell for as high as you believe people will pay.