I would like to suggest that a kind of market notice board is set up near spawn, players would be able to leave signs on it saying what they would like to buy and for how much, and if someone likes there offer, they could put "offer accepted" and a time to meet at the notice board for the transaction. Or alternativly set up an area for chest shops.
Yes, this would be a good idea. You could arrange times to trade too so that nothing ls left in locked/ public chests.