Poufny, you can sell your Djinn-items in the house east of Thais Depot, to the NPC Nahlesar, but it's 50% cheaper prices there, so for example, you will sell knight legs there for 2500gp, which you can sell for 5000gp to the real Djinn NPC.
So if you want the real price, simply do the quest and sell them to the NPC's in Ankrahmun.