A noble merchant operating under the auspices of Tunon's administration, Pentibor was one of the few lucky enough to receive a license to trade in a great variety of goods, including weapons (a particularly rare honor). While trailing the Disfavored contingent is hardly the easiest life, he doesn't complain, as it gives him the opportunity to make a good living, rather than try to maintain a pitiful stall in the Bastard City with his niece, Rhona.
Beyond the standard trading, you can always try to take advantage of him. Subterfuge 20 allows for getting 10 copper rings. Lying about peddlegrass allows for extortion of a sizeable Ring donation.
After talking to Iron Marshal Erenyos, you can receive an iron helmet, breastplate, or sword from him for free.