Well, short of standing guard at the door (which I don’t think shop owners would particularly appreciate), I don’t know what we can do. It’s really up to the readers themselves. At some point, people have to realize that they’re wasting their time, their money, and their very lives to read this trash… right? RIGHT?
I’ve also tried turning people onto non-superhero comics, with very limited success. For everyone I convince to give Eisner or Spiegelman a shot, there are five more who say, “Yeah, I guess I can see why it’s good. I just like Spider-Man better.”
Sin City seems to be sort of a gateway drug. You can turn superhero fans onto it because it has action in it, but it’s not a superhero book and it has non-superhero antecedents. Plus, people recognize it from the film adaptation.