We have been plagued by Rad Scorpions for some time now. All who have been sent to destroy these monsters have not returned. I will give you weapons and armor if you will follow my guide to their lair and kill them all.
The Barterman is a trader who was originally intended to initiate the Stop the Radscorpions quest by sending the Vault Dweller off with Sammy as a guide to their location, in hopes he could destroy them. He was cut from the game and Aradesh apparently replaced him in his role.