Make game shopping fun. Don't focus on upselling/diverting customers to used copies. Just create an environment that is comfortable full of knowledgeable, non-awkward associates who know gaming's history and its present. Remind them to check their egos and their biases at the door, and simply be good salespeople that have the consumers' interest in mind. Conduct regular tournaments, and not just for Smash or Mario Kart. Speedrun tourneys are also fun. Do cosplay contests or DIY craft contests, and don't be afraid to advertise these to the local public. Be a cultural entity and rise above the standard model.
Reward customers for their used purchases and still make a killing reselling to the next. Have a buyer's reward club where any 5 new purchases gets you a free used game of any value.
There are plenty of ways to create a sustainable marketplace. The fact is, gamers are rabid consumers and place like Gamestop and Toys R Us just aren't taking advantage of that ecosystem to its fullest. It takes work and dedication and energy, but it can be done. The key is the staff. Hire well. And no, that doesn't mean the same thing as pay well. The right job with the right atmosphere will make many a great employee accept a standard or minimum wage to be part of the show.