Caduceus is an item. It is part of a group of items collectively referred to as Artifacts.
Passively grants Haggle Expert.
Sell an item to another player for the same price as the Pawn Shop. If that player doesn't have enough money, they'll pay you all their remaining Rupees for it.
Alternatively, target a player to see 4 random items from their inventory. You may choose to buy one of these items from them for 70% of their base price.
The famous staff of Hermes, messenger of the Greek Pantheon. He was, among many things, the god of trade. It was said that during negotiations, the eyes of Caduceus' snakes would glow, which would ensure a positive outcome...