Free To Play: You're Doing It Wrong

If your game makes it absolutely or next to impossible to progress without explicit purchases from the cash shop that you cannot earn yourself, be it through hard work or purchasing the necessary items from other players, you are giving your player community the finger.  Absolutely everything in the cash shop that is necessary for play should also be available without spending real cash.  Break that rule and you've crossed the line from caring about your player community to blatant greed, and you've sold out your integrity.