I love this question. From my own perspective,i would say there are many ways mapped out for such:
- Tripleclicks: You get your commission when you sell stuffs at no cost.
- Referral program: you get paid when you refer/register someone.
- Act of duplication: The most powerful means to achieve success at very little or no cost. Get paid when your sponspored affiliate(s) make any purchase/sales.
Hope this helps.
Best regards