I dont know if this has been suggested or not but
I would like to add a suggestion that the game should have a reverse shop: a shop where instead of spending coins to get an item, you give an item to receive coins. This exchange where u trade an item for coins has already been made possible with the trade portal but, I think that having a shop that can do the same thing encourages more player interactions and trade than just relying on a trade portal. This would be a great addition for server focused more on an economic gameplay.
Another thing I suggest would be an addition of a barter shop. For this, u trade in an item for a different item instead of receiving coins like a normal shop. The reason why I feel this should be added to the game is that based on my experiences, players conduct this kind of trade on PvP servers. The problem is that on those servers there would be a third party (like me for example ) who would use that opportunity to attack and disrupt the exchange. Another problem is that one of the participants of the said trade could double cross the other by not giving the item he or she promised to trade.