@Alexander.Tenshii
NPCs are the only source for Shell II and, as a scroll, it is consumable.
Buying it on the auction house means that auction house fee has also been removed from the economy. SE takes their cut, it isn't a straight player to player transfer of gil.
Buying it from the source is cheaper, but either way gil leaves the economy.
@Unicorn.Iain
You've obviously failed the school of ffxi basics.
Buying items on the AH does NOT remove the money from the economy. Seeing how the money goes towards a player. Unlike buying from NPC's where the money is instantly gone.