Fallout 4 Merchants

Merchants can be found in various locations throughout the Commonwealth in 2287.

Background
Merchants are the primary source of buying and selling goods within the Commonwealth. Multiple merchants can be found in major settlements such as Diamond City, Bunker Hill and Far Harbor, but others can be found in unmarked locations. There are also traveling merchants who can be found around the Commonwealth. The most significant traveling merchant group is Stockton's caravan run by Old Man Stockton in Bunker Hill.

All the major factions have their own merchants based at their headquarters. The Sole Survivor can build stores at allied settlements once they have the Local Leader perk at rank 2 to expand the total number of merchants available.

Merchants
Caps values vary randomly between inventory refreshes, like inventory does. The caps numbers listed below are indicative values only, unless marked with an asterisk, in which case they are verified from the game code. 'Base caps' means that every effort has been made to exclude the effect of the Speech bobblehead (+100 caps) and Cap Collector rank 3 investment (+500 caps). Values for Bunker Hill merchants can be +300 to +600 higher dependent on certain quest completions. There may be a similar but lesser effect for Covenant merchants, if allied to the player character.

Notes to table
0 : no effect from the Speech Bobblehead 1 : 50% chance 20, 50% chance 20-29 2 : double effect from the Speech Bobblehead 3 : up to +300 for Bunker Hill quests 4 : up to +450 for Bunker Hill quests 6 : up to +600 for Bunker Hill quests P : Pool - caps and items are shared with other trader at the same store R : Replace - trader replaces/is replaced by other trader at the same store S : Settlement traders of the same tier and type share the same global items and caps. Higher tier traders share all the inventory and caps of all lower tier traders of the same type (but not vice-versa).

Settlement merchants
The addition of the settlement system in Fallout 4 allows one to assign any settler to a store, allowing the player character's own merchants to be created. Depositing a small amount of caps over time to the workbench, they allow another avenue of various shipments, junk, weapons, armor, aid, ammunition, and clothing beyond pre-existing and wandering merchants. They also create opportunities for the player character to sell surplus items for caps, and some of the stores can also increase settler happiness at the settlement. See details in the article on stores.

Unique settlement merchants
In addition, there are eight unique settlement merchants in the Commonwealth, who are unofficially dubbed as "level 4 merchants" or "tier 4 merchants." These NPCs will provide much better equipment and junk than normal settlers, including the sale of unique (legendary) armors, but only when assigned to tier 3 stores.

Some of these merchants can only be recruited to a settlement if the total of its own population, and that of all settlements connected to it by supply lines, is at least a certain amount, with the largest demand being 30 people.

Though the Vault Dweller's Survival Guide for Fallout 4 claims Holt Combes can be recruited as a vendor for settlements, he actually has no special shop assigned to him in his game file, nor any settler variables set in place. Tina De Luca, another Vault 81 dweller that can actually be sent to a settlement, has partial variables set in place to act as a specialty vendor.

Shipments
Some merchants offer bulk shipments of crafting components in their junk category. Shipments are of 25, 50, 100, 200 or 250 units depending on the rarity of the component. The unit price of shipments is usually higher than buying individual items that contain the desired component. However shipments allow you to obtain large quantities in a predictable way. This can help with large scale crafting, or as a way to get rare components for crafting advanced mods. Common components (Wood, Steel, etc.) can be obtained for free by scrapping objects in the build areas of owned settlements.

Shipments use up no carry weight and can be placed in personal inventory or in workshop inventory. They can also be consumed over supply lines. When used for the first time, the shipment is broken down into the specified number of items, which are deposited in the current location. From that point onwards the items have weight and so it will use carrying capacity for the player or NPCs to move them.

Unlike other merchants who offer shipments, Alexis Combes always has only one shipment available at any given time, but which item is in the shipment changes. Saving the game before trading with her allows one to load that save for a different shipment or one can wait/sleep for 48 hours.

Bugs

 * When trading with Trashcan Carla and/or some other merchants, the caps transaction will not be accounted properly which results in loss of caps. Then, the bug seems to carry at random. Fix: Remove all charisma boosting clothing and then put it back on, speak to the merchant, exit, then try to buy from the merchant. Try selling one or two rounds of items to make sure the price is right.
 * Some Level 4 merchants will not travel to or stay at a chosen settlement after being assigned there. Solution: after the merchant has been assigned, disable them and any other traveling companions they spawned with, such as accompanying mercenaries ("prid [ref id]", "disable"); fast travel away from the area they spawned in; then walk, don't fast travel, back to that exact same area and a different random encounter should occur, such as wild mongrels or synths; if so, re-enable the merchant ("prid [ref id]", "enable"); fast travel to the settlement; and finally, move the merchant to the player character ("prid [ref id]", "moveto player"). Now the merchant should stay put.
 * Holt Combes is listed as a Level 4 merchant, but he cannot actually be recruited to a settlement.