Well, I don't much care for censorship. But is this "censorship"? They aren't a government or anything. They run a store, essentially. And sell what they feel like. If somebody doesn't want to alter their book to fit, they don't have to.
It makes sense that a retailer has the right to choose what's on his or her shelves.
What if it's something that might make him legally liable? What if it's a slur of his religion or race? What if he doesn't like books about lesbians or elves or algebra?
Should he have to carry them?