Before I give these ideas I have a few words, don't troll on this post.
Idea1-Player Shops-For 500ec a player can make a shop, people can view and buy from this shop by clicking on the person and it will have a option 'shop'. That's my first idea.
Idea2-Auction Houses-An easier way for people to buy items, the auction house, the option is opened from the menu. People just put up items and they get sold under categories.
+1 for the auction house :)