Merchant

Merchants are the primary source of items and equipment in the world of Fallout, aside from dead enemies. Merchants operate out of either fixed stores or traveling caravans.

Fallout and Fallout 2
Most NPCs can be bartered with. In addition, almost all friendly towns have 1 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 and San Francisco. In both Fallout 1 and 2, the further south they are the better stocked they tend to be. The Gun Runners have the most advanced weapons in Fallout 1 while the stores in San Francisco have the most extensive inventory in Fallout 2. Shops specializing in other wares can be found.

Traveling merchants can be found traveling the wastes in guarded caravans. They usually sell assorted merchandise but can occasionally offer a unique item.

Shops and merchants in Fallout
Vault 13 Medic, Razlo, Darkwater's, Gizmo's, Doc Morbid, Hub General Store, Library, Iguana Bob's, Beth's Gun Store, Maltese Falcon, Old Town Arms Dealer, Vance (drug dealer), Thorndyke (healer), Water Merchant Vendor, Brotherhood Doctor, Tine's General Store, The Gun Runners, Cathedral Gift Shop, Dr. Wu

Fallout 3
In addition to General stores and Medical Doctors most towns also have a food vendor/bartender as well as one person who can repair items. Clothes shops can be found in richer settlements. Weapons/Armor shops are found in Rivet City, The Citadel, and Paradise Falls. Rivet City also has a dedicated Chem dealer.

There are four caravans traveling the DC Wastes. One dedicated to food/chems, another to weapons, another to armor, and the last to junk items. They can be invested in to improve their selection and repair skills but they are vulnerable to attack. In addition to the caravans, Wastelanders can be found who will sell random items or sometimes rare items. Some special encounters with doctors, chem vendors, and hunters (food vendors) are also possible. Inventories will scale by level but certain advanced items like advanced power armor and plasma weapons remain unavailable. Price, aside from discounts appear to be constant across stores.

Merchants have a new inventory after a period of three days, and then again after a period of four days, in order to correspond with the length of a week. The inventories update at 12:00 AM the day of, although which days these updates occur vary from player to player.

Infinite caps glitch through merchants
This glitch will allow you to get an item repaired to 100% for free and it will also allow you to make free caps and ammo as long as you have one item and the shop keeper has one of the same item as you. Or if the shop keeper has two of the same items and you have none (same condition is not required).

1. Go to a shop keeper and trade with them

2. Make sure the shopkeeper has at least one of the same item as you are trying to sell. Or that the shop keeper has two, and you have none.

3. Sell your item to the shopkeeper. If the shop keeper has two of the same item, You can skip this step.

4. Buy the cheaper of the 2 items back (nothing happens the first few time)

5. Sell the same item back to shopkeeper and then buy it back again

6. When you buy the item back you will notice that for you, it is fully repaired. (If it is only partially repaired, repeat step 5 until it is fully repaired).

You can now sell the fully repaired item back for a price that is higher than the price you bought it for. It will remain the same condition and price as when you first sold it in the shop keeper's inventory, but will be fully repaired and worth more when it is in your inventory. The reason the repair is free is because you can repeatedly buy and sell the item for a profit, negating the initial loss of caps that you encounter when you first buy it back.

Say laser pistol "A" is 24 caps but laser pistol "B" is 300 caps. You are now making a profit of 276 caps every time you sell it. Even though you are buying the laser pistol for the price of 24 caps you are selling it for 300 caps and making money. To take this one step further, You now take the caps you just got from the shop keeper and use them to buy any items you might want like health items and ammo. Now keep buying and selling the laser pistol back and forth like before until you get your caps back.

When the shop keeper runs out of caps, ammo or any other item you might want, Just hit the back button and wait 4 days (Right there in the Shop) and the shop keeper will now get all their items and caps back again. Repeat all the above steps over again as many times as you like or need.

Note: It seems this will only work if the two items are of the same repair level. This will make the items in the merchant's inventory appear with a (2) beside them rather than two separate items (and the items will be the same price initially).