If your poop contains the kind of microbes that make it suitable for transplants into patients who "need healthy fecal matter in their gut in order to survive," a company called Open Biome wants to buy it from you.
They’ll pay you $40 per sample, plus an extra $50 if you come in 5 days a week (the donations have to be made on-site.) The only thing is, you have to be super-healthy: only about 4% of prospective donors make the cut.