Gamasutra has an article about GDC Europe, where Teut Weidemann from Ubisoft talked about "exploiting human weakness" to monetize Free2Play games. He lists those weaknesses in the form of the 7 deadly sins (which by the way are NOT in the bible, but have been invented by the catholic church in later centuries), and how they can be monetized:
Vanity: Selling player items used to show off.
Envy: Selling players items that allow them to catch up or overtake other players.
Gluttony: Selling consumables.
Lust: Selling instant gratification to bypass a wait.
Anger: Selling items making the player stronger for PvP.
Greed: Selling player resources or buff for faster resource gains. Teut recommends not selling currency directly, not not trigger player's sense of unfairness.
Sloth: Selling stuff that saves the player some clicks.
While this is strong stuff in a frank talk, of course all of these tactics to exploit human weaknesses are instantly recognizable as being already implemented in various Free2Play games. This isn't a devious new tactic, but more of an inventory of what is already out there. So I'd say Teut is doing us a favor by spelling out the deadly sins we are probably not admitting to ourselves when we buy stuff in some item shop of a game.