It probably is a little high. Problem customers get more attention than non-problem customers, so I am sure that colors my recollection. Some of those problem customers have specific problem behaviors. For example, the anger management guys were fine... outside of a competitive environment.
That said, I would not be surprised if comic/game stores do not have a slightly higher than normal percentage of problem customers. I cannot imagine the stealth competitor existing for a lot of other business models. What? Some guy is gonna lug a box of books into a bookstore and try to undersell them? And how is anger management guy's issues going to come up while he's buying tools at a hardware store. Some are directly related to the fact that people like to come hang out at a game/comic store. People do not hang out a grocery store, so you'll likely never have to endure the sexist/porn idiot there.
Some problem behaviors are huge for any store. The numbers on shoplifting are staggering for a lot of industries.