Step 1) Track the Gil and ban those who trade with the sellers. Come down HARD on those who buy the Gil, put the fear into them. Buyers should be priority target as no buyers=no sellers.

Step 2) Watch the sellers migrate to something worth paying out for accounts after SE destroys their market on FFXIV.

It is the Gil buyers that keep the sellers buying acccounts to farm and ply their "wares" in game. To be honest, for me, they are worse than the sellers, sellers just take advantage of peoples laziness/stupidity.