Most non-player characters can be bartered with. In addition, almost all friendly towns have one or more merchants with a substantial and replenishing selection of items for sale and a large amount of caps. The general store is the most basic shop and can be found in most settlements. Doctors sell medical supplies and are also present in most towns. 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.
All merchants in Fallout do not restock, except for bottle caps, which are restocked instantly.