From what I've seen, servers only seem to accommodate communication between you and 20 other users at any time. If they ever do add advanced filtering, this would screen out items you're not looking to purchase.
I think that when they remove travel to other cities, it should provide a subsection of other items that city sells if they have asked those items to be advertised. If the item no longer exists, however, the system should replace it with stock from another city that also sells it. The amount of items you can advertise before waiting should also be increased to 2.
