There is a really simple solution to RMT.

Remove all references to gil from the game.

Make players farm stuff they want themselves.

Make all gear tradeable.....

... Then change the market board so people can just "list" gear they want to give away for free when they are done with it.

Crafter's can still craft and help their friends. They can't make gil? So what. Do it for fun. Farm materials and craft. You will be needed to help supply your FC giving the jobs meaning.

Gil is a redundant concept. Let's banish it forever.

No cost. No gil. No RMT. No problem.