The Mystery of Virtual Economies and Online Social Networks.

In the disclaimer on a social network, it is stated, that credits purchased have no monetary value.  So what that is saying is that a customer gives money and gets nothing in return.  And with nothing purchases a right to read and write a letter, view a picture or a video.  Which have no value.  It costs the company nothing more to give a customer 100 credits or 1000.  What it buys is customer satisfaction.  A satisfied customer give the enterprise money for nothing.  An unhappy customer does not.  Make customers happy, make money for nothing.