I was having the same issues and found this thread:
http://eqiiforums.station.sony.com/eq2/board/message?board.id=Newbie&message.id=1427
You can only sell ig you buy a markey bulliten board in east freeport (don't know where in qeynos). Put that in your room and set up shop. To buy you must buy from a broker or go to the place where the seller is selling. Note: when you click on a house/inn where you don't live and want to visit someone, you have to right click and select visit from the menu. I was stuck for a good 30 minutes trying to not buy a new house when all I wanted to do was buy from someone.
It's a very realistic, labor intensive and silly system for a game. You even continue eating food/drink while /afk in trader mode, which is enough to run you broke you you don't make any sales.
____________________________