I think shouldnt exist marketplace, there should be trade to player-player, you can ask in world chat for exemple: I need this or buy this or that and the seller or the buyer go to the localitation of the seller/buyer, that will made a good ambient on the player's made them socials, etc...search an item on marketplace made feels something empty.
That's an incredibly bad idea. One argument - what do you imagine will happen when the server fills up and a lot of people start spamming in trade chat for whatever they need/want? It'll be too fast to follow and it'll be annoying.