The Arms Dealer is an NPC vendor that will spawn once the following criteria . seem to argue with each other through Emotes, implying they don't get along. How to Get the Arms Dealer in Terraria. The Arms Dealer is one of the most important NPCs in Terraria. He sells you ammo, which can be hard to come by, and. The Arms Dealer is an NPC that will move into a suitable house once the player has a firearm of any kind. The fastest way to get the arms dealer to move in to a.