Apparently there are named settlers scattered across the commonwealth that you can recruit. In doing so, if you assign them to a level 3 vendor, it will be upgraded to a level 4 vendor that can sell even better gear.
For example: Ann Hargraves
Who and where are the rest of these named settlers?
Also, how does this affect the stock when you have multiple vendors of the same type?
Small spoilers:
The vault tec rep boosts whatever vendor he's assigned too but not to the level of a level 4 vendor, what happens if I have him and a named settler assigned to the same type of vendor?
Best Answer
The Vault-Tec rep boosts the trading emporium - that is what he should be assigned to. Some of them have unique items to sell which is why it is a good idea to collect them plus they also have better standard equipment.
There is a full list of the T4 vendors and what they should be assigned to here.