At pawn shops I always haggle, it's expected. At one in particular, the new guy there was helping me with a used shotgun. Before we even discussed "my" price, he said he'd heard of me and that my negotiating skills are legandary
At the LGS, on new guns I don't try to negotiate, not much markup on new. On used guns I always ask if there's any wiggle room. If not and it's in my price range I buy, otherwise it stays where it is.