As a follow up to my last comment left here, I'll note that social protocols, shunning, shaming, etiquette, peer pressure, customs, taboos and the like have all proven highly effective at regulating human conduct outside of governments and markets, and even often within them. In other words, reputation plays a key role in all successful commons.

Essentially, as is currently evolving right here on Steemit, the "community" comes to "agree" on certain customs, taboos and ettiquette designed to protect the commons from being exploited while also making it available to all in a "fair" way. Those who violate the agreed customs, taboos and ettiquette are shunned or shamed by the overwhelming majority. This shunning/shaming makes life more difficult than it need be for the violater. Eventually the violater learns that life is better following the custom than evading it. We saw this right here on Steem when the new reputation system was unveiled. People with low reps were marginalized and mostly either left the ecosystem or begged for forgiveness and agreed to modify their behavior.

It doesn't perfectly prevent individuals from exploiting the commons, but it does it well enough to be effective in most instances. And technologies with built-in reputation systems, like Steemit, will make that even easier in the future.