Another idea:
Delivery could be a user mission given as a quest if the player happens to inquire about a quest at a station that happens to have the requested item within some server-configurable radius of the item request.
If no-one picks up the quest in a server-configurable time limit (e.g. 15 minutes?), an AI trade ship takes it instead.
It'll delay the delivery by at least 15 minutes, but could give the universe a more "living" feel.
Further ideas:
If the quest player fails to deliver the requested item to the requesting player in a server-configurable time limit (1 hour?) maybe something else could be triggered to make the situation a little more interesting. (Maybe add to the questing player's bounty, so other players hunt him down, and add hints to NPC shopkeepers to give players on where the requested item might actually be located, and maybe offer a new quest to someone else to deliver a new instance of the requested item to the requesting player.)
In the meantime, the requesting player is getting impatient. Maybe there could be something further they could request. (Maybe the requesting player could demand immediate deliver by trade guild ship at twice the price, with no player quest given! This could allow the requester to end up with more than one of the requested item.)
So this could really create some neat player-influenced content to make the universe more dynamic.