To be honest, Aeria is at the best position to reduce buying and selling. Being in a FTP model puts Aeria at an advantage. Last Chaos for example -- premium items are sold at a price that many selling sites can't compete with. Gold is something that does not flow freely (which I agree it shouldn't) so it gets hard to combat it. Aeria can start selling gold through the cash shop, but it would compromise the game.
If aeria can appeal to reduce the demand of gold buying within its games through incentives (bannings people who do it on a consistent basis, education posts such as this) then they stand to combat it effectively. Without the demand, gold buyers will pack their stuff up and leave. Right now Last Chaos has effectively and temporarily combated spammers -- but this was with the help of the community and new game devices.
At least that is my humble understanding... Gold buying is the same as cheating to me. I really hate it and if you need to cheat in a game, then just don't play. Find something easier.