Borderlands: Game of the Year Edition
81 Achievements
64-76h
Fence
Sold 50 guns to a shop
53.5%
How to unlock the Fence achievement in Borderlands: Game of the Year Edition - Definitive Guide
You can sell any gun at any of the vendors (medical, ammo, weapon)
The easiest way to get weapons is by killing enemies and looting the red large crates.
The 50 required is an accumulative total, so you don't have to sell them all to a specific vending machine. Any vending machine will do.
The amount of weapons you will find throughout the game is almost beyond count. To unlock this achievement be sure to pick every weapon up that you find and if it's something you don't want, sell it to a vending machine. There are vending machines in every area and they are on your map if you forget where they are. You will unlock vending machines very early on during the opening missions of the game so you can begin to sell unwanted weapons almost immediately.
The trophy description for this trophy is slightly misleading as there are no "shops" in the game per se, just Vending machines though they will say "shop" when you place your crosshair on them. There are 3 different Vending machines in the game and you can sell anything to all 3 of them.
This trophy is cumulative so play normally, sell everything you don't need and you should get this trophy early on.