vinney...axkl on Nostr: Some autonomous process whereby each participant injects small "secrets" into ...

Some autonomous process whereby each participant injects small "secrets" into products or information they share around or trade, and their software keeps a list of who has been given which secrets.
If information is leaked/snitched out, the originator of the secret can cryptographically prove (to the other members) who the rat was.
The credible threat of the above might be enough to keep people "honest".

Or... you just can't scale up illegal economies that much, don't try? Be content with local food and other consumables, traded on the grey market.