Games are like cars. When the new model comes out everybody wants to buy one and the price while reasonable can be a little high; as time progresses their value depreciates until they're practically worthless, especially if people hold onto them. But some games are hard to come by for various reasons and that rarity increases their value (unless the game sucks so hard it generates its own event horizon). Given that the condition of these rare games will vary wildly I don't think trying to offer the same price as if it was in 100% mint condition unplayed with 1,000,000 other copies out there is a sane thing to do.
So no, there should not be any regulation on the used game market just like there's not any regulation on the antiques market. You pay what's being asked and hope you don't have a counterfeit on your hands.