Like many others who posted, I don't waste my time haggling in the big box stores. Usually the price is set at minimum profit, but mostly because the employees don't give a sh*t if you buy something or not...they get paid the same (attitude).
Gun shows I always haggle. I feel if I spend the gas, admission and parking fees there should be some consideration. I tell them "if you are not willing to negotiate why should I just not go to one of the local stores for the same price". I will not buy from someone who is not willing to deal at a gun show.
I find small pawn shops are most likely to deal. Pawn shops generally "own" the gun (if used) for VERY little money. A friend in the business once gave me an example using an nice Remington 870. The guy pawning the gun will only get @$50. If it is not taken out of pawn they sell it using retail gun prices. The longer the item sits the more willing they are to sell. Don't be shy about making an offer. Most will look up how much the item cost them and negotiate.
I just picked up a really nice Marlin 336 last week in a little mountain pawn shop for $240 plus tax. The tag on the gun was $430 and I offered $200. We settled on $240. Happy haggling!