Making something hard on RMT is the same as making something hard on regular players, because they're pretty much identical, except for the whole selling of virtual assets thing. You cannot penalize one without penalizing the other.
Focus first on having a sustainable economy. There are some excellent points made in this thread:
http://forum.square-enix.com/ffxiv/t...-are-Worthless
The summary is that items should be leaving the economy at roughly the same rate that they enter it, gold should be doing the same, and trading of items between players should be easy.
By leaving the economy, I mean getting sold to a vendor, thrown out of the inventory, or disassembled for materials that could not be obtained any other way.