In a fully decentralized environment, you would need to somehow know who to trust and make some karma/feedback in a decentralized way.

Given that PGP's web of trust never really caught on, I am not sure if this would work.

But maybe it would and I am just too pesimistic.

The pirate bay has a comment system, and an option to verify torrents are uploaded by someone. It's possible to implement those in a p2p way, but than it comes close to the improved systems on silk road with reputation ,etc - so maybe they prefer not to go there.