The game won't have it because it wouldn't be a good business decision by Eurocenter. The way the game works now, money is spent in shops and disappears in exchange for a hat/item which means it's gone forever and players need to work/buy gralat packs to get more. If there is trading then money will circulate throughout the playerbase instead of being spent on shops. Also, people won't go to any old shops because the same item from that shop would be cheaper when buying it from a player. So, less irl money spent in game.