Barter

Barter is a skill in Fallout, Fallout 2, and Fallout Tactics: Brotherhood of Steel.

Trading and trade-related tasks. The ability to get better prices you sell, and lower prices for items you buy.Your reputation and reaction from the NPC will modify how they deal with you. If you have a good reaction with the NPC trader, you will get a better deal. If he doesn’t like you, you will pay for it – literally. Your Barter skill, however, is the primary factor, along with the Barter skill of the NPC. Initial Level: Starting Barter skill is equal to 20% + (2% x Charisma). Average characters will have a 30% skill.

Having the "Master Trader"-perk will give you 10% bonus to this, although. The "Good Natured"-trait will give you additional 25% on the Barter skill.