You should have at least one rogue in your party, for picking locks and pockets. Get the thief's pickpocket skill up to at least level 4. Then, find an item that is relatively expensive which an NPC (Not someone in one of the town stores!) will buy. Sell the item (it helps if you have more than one), and then get the thief to steal it back. Sell it again. You can do this as much as you want, but save frequently (everytime you successfully steal something is suggested). I used four Dragon Armors on one of the dwarf workers. I averaged about 9000 gp every minute.