• Kill people for money
• Sell drugs (seems to be a big one)
• Sell counterfeit things
• Sell items with a higher cost outside of your country for in between
• Scam people w/ the above or creatively

Please correct me if I'm wrong, but it would seem that besides operating an illegal business, any means of making money available on Tor would be available on non-Tor, because all it does is offer a thick layer of anonymity and any online money making websites would probably want to block nodes because of country-specific restrictions.