Kill selling, the latest crafted gear and materia prices are the 3 major markets for RMT gil. Anyone who thinks otherwise is kidding themselves. After all, those are the 3 primary things that actually cost any amount of gil. Given that 90% of a server population can't make that much gil from crafting or selling kills themselves, coming across players dropping 20mil, 30mil, 100mil on a kill, it's pretty clear where that gil has come from, even if I've not been told by those doing the selling, or friends of the buyer, that the gil was purchased.