>Diablo : selling items to players is fair because blizzard is not selling the items.
>Star citizen : selling ships is fair because it will stop after the game comes out (please ignore the planned in game cash store).
>LoL : selling champions is fair because you only use one at a time.
>Hearthstone : selling cards is fair because its expected from a card game.
>Guild Wars : selling gold is fair because the game has no subscription fee.