Most non-player characters can be bartered with. In addition, almost all friendly towns have one or more merchants with a substantial selection of items for sale and a large number of caps. The general store is the most basic shop and can be found in most settlements. Doctors sell medical supplies and weapons and armor merchants can be found in larger settlements such as the Hub.
Generally, the further south they are found, the better stocked they tend to be. The Gun Runners have the most advanced weapons in the game. Shops specializing in other wares can be found throughout the wasteland. All merchants do not restock their wares, with the exception of bottle caps, which are restocked instantly.