Bobblehead - Barter is a Fallout 3 item, a Vault Boy bobblehead. It permanently improves the Lone Wanderer's Barter skill by 10, to a maximum of 100.
It is found in the Evergreen Mills bazaar, in a dark cave-nook, in the corner of the room to the right of Smiling Jack. Jump over the workbench, and it's on the right-most shelves.
The bobblehead shows the Vault Boy holding a Nuka-Cola bottle cap, even though the bobbleheads are supposed to have been made before the Great War, when bottle caps were not currency.