Quote:
You may not sell, purchase or exchange for real-world money or value any in-game currency, accounts, characters, in-game services, or in-game virtual items.
Translation "All content within the game is property of Square Enix, and is not your legal right to sell for real money."
Quote:
You may not play the Game for the purpose of acquiring virtual items or advancement in game play on behalf of a third-party or for the purpose of selling any virtual assets to a third party for real-world money, specifically including "gold-farming" and power-leveling services.
Again, this applies to the actual real world trade of money for in-game services not sanctioned by SE. Buying Gil, Crysta, or any materials with US Dollars (or Japanese Yen, or Euros, etc) is where the violation comes in, if it's not directly from SE. Since only Crysta is sold by SE, you can not legally buy any in-game item from another player for cash.