We are now in a world of online commerce. It is important now for kids to learn how the Internet and online commerce work. There are certain principles that remain true regardless of what times we are in. One of the most fundamental principles of commerce is "trust". This is where words-of-mouth is still one of the most important elements of selling power in this online world.
Past users of Mathemafix carry this marketing power. People believe what they say because they were successful gaining places in top schools. To harness this trust, credit will be offered to past (and present) users who introduce new users to the OC or Selective support groups. Current users get credit to extend their subscriptions. Past users get PayPal credit paid directly to their PayPal accounts.
All one needs to do is to introduce this website to others and tell them to put one's login id as the referrer (during registration).