There's a right and wrong way to do it.
We charge way below MSRP on our stuff. We've got the best prices in a very wide radius, and if we relied just on selling guns, we wouldn't be able to make rent. Most of our money comes from the range.
(Eastman does gun shows twice a month out here, and our prices are better than anything folks find there. In fact, we have people coming into the shop with their "find" from the gun show who come in, look at our price and go, "drat!")
Truth be told, we'd make more money just doing a transfer in many cases. That's how small the margin is. We tell people that when they ask. We're even glad to show them the actual MSRP compared to our prices. Most are understanding, but some folks still insist, and they're usually pretty obnoxious about it.
Asking, "is that the best you can do?" when a gun's at MSRP makes sense. Pestering about it when it's as much as $200 below (look at S&W's MSRP. Robbery.) is just rude.
When some guy who I've never seen before walks in, pesters the help for an hour, picks the cheapest gun on the rack, then insists that the only way he'll buy it is to sell it below cost...no thanks.
OTOH, I've been to some stores that are just ridiculous on their pricing ($750 for a Glock). When you haggle them down to something resembling sanity, they act as if they're bending over backwards to make a "sacrifice." The whole thing is dishonest and frankly, I'd just as soon not deal with that song-and-dance.
Sadly, that's a very common practice for gun shops, and people with some experience expect to get ripped off. I don't mind a little frugal poke, but pushing when someone already knows they're getting a good deal is just greedy.