Hi,
not absolutely sure how it works but it does seem sometimes if you try to sell something that a particular vendor would not really need, such as plate-mail to a potion seller, then they will not give you any gold.
However, it seems the old Guy in the room to the left of the bar in the Inn (can't remember the Inn name, Crab something?) will buy just about anything! Lower room to the left of the stairs.
Hope that helps
