Is this possible?

[Tabasco]

I don't know how the client would respond to a trader request outside of a bazaar 'water' area, but I can speculate that they had you stand still in a stall for a reason. Someone with more knowledge of client behavior might have some insight on using existing merchant functionality.

On the other hand, players could spawn an NPC with their wares in a defined area (you could use perl to establish that in a zone) and other players could hail that player's merchant for items and prices, not unlike many Asian MMO's.

I took the route I did because even with saylink menus the interface is going to be clunky and I wanted people to be able to buy and sell without logging into the game. In fact, the bulk of the commerce on my server is done while people are at work.

At the very least I have a good chunk of item validation code that you would need if players are going to be able to do inventory management through an NPC and the quest system.
If you can lay down a better overall design for the behavior you're wanting I would be happy to help.