When did this happen, and what's your source for it?
The closest thing to an official public position that I've seen is that buying just to resell (flipping) is against the ToS, and so is selling for "exorbitant" amounts of gil. In the end it's at the discretion of the GM's, and they need some kind of in game evidence of the sale as well as someone reporting it. If your transaction is done outside the game's chat system, you're highly unlikely to get reported or punished.
