I love the idea of player stalls it adds much more player interaction and price fluctuation than auction houses. The idea of having bids on stalls for certain items is interesting but I don't think it's really necessary as we've done well with just a chat box inside the stall in other mmos where you can leave your bids along with CoD mailboxes for the winner. Doing it this way causes more player interaction than purely automating everything which to me makes mmos feel more immersive and not just singleplayer RPGs with other players running around.
Also having certain item that you can get in a dungeon or raid that allows to leave your stall open for X amount of time while you're still playing would be nice.