You know how you kill the plat sellers? I'll tell you.
You cannot destroy them by going after the farmers. Ban em, they just come back. They're like roaches. You need to go after what they feed on.
You need to go after the Johns. Publically. Buying plat is against the TOS. Make a statement that the TOS WILL BE ENFORCED. Ban accounts of those that buy plat. Make it public. Publish names of characters. Make sure that everyone understands that if you buy plat, you will be shown the door and invited never to come back.
Problem solved. Plat farmers have nothing to feed on, and they go away.
Unfortunately, no company seems to be willing to do it. They'd rather have their in-game economy borked all to hell and back. I don't understand that. Instead we have all these mostly ineffectual systems to try to control the roaches (although the mail system works, I'll give them that, it was a brilliant move).