I never knew of zappers. But I do have a lot of nostalgia for some old game stores.
My favorite and probably first game exchange was Mauck's game exchange (spelling is probably wrong) in Tulsa. It is still my favorite. He always had what seemed like odd prices for games. They would be like $4.62. And I always thought they were really weird and specific prices. But he made it to where after tax, you paid with a whole bill. It was the place I bought my power pad. It was where I saw my first ROB unit. They also sold old game magazines. Moreover, it was where I learned a lot about games. How to clean them, etc. The people who owned it were really nice.
It then changed to Hershels or something like that. It seemed nice enough, but I admit to not going there much. Now it is a tattoo parlor. :-(
I loved Funcoland.
In Boulder, I moved right across the street from a fantastic game exchange called game force. Reasonable prices. Plus, he had good stuff all the time. Most places in Tulsa are majorly picked over. Game Force in Boulder always made a point to seek out and keep good stock. Thus, the prices weren't mega cheap. But they were very reasonable. If you wanted a good game they would have one.
Game Dude in North Hollywood has a lot of good memories. As a kid (and sometimes even now), I would always look at their price printouts (kind of similar to the funcoland newspaper. I suspect they are from the same era and persuasion).