It's simple okay. Just lock items to the world they came from. Give them a world signature or something. So if item X was obtained (crafted, bought, dropped, etc) on Moogle for example, it should get the "Moogle" signature and only be able to be sold on Moogle. You should still be able to use or wear the item, but not resell it. Simple solution to this problem.

The whole Chaos data center is flooded with JP items sold by bots who just keep transferring Home World. So A: prices for those items on Chaos drop significantly, and B: you are automatically being undercut every 10 minutes so good luck selling your item. It's funny that I (players in general I guess) am able to figure all this sh*t out by myself, yet SE seems to have no clue. Even after handing SE all the retainer names of the bots and proxy characters used to buy the items on the JP data center nothing happens.