#Matrix sharing their view on decentralized reputation as a spam and abuse prevention tool https://matrix.org/blog/2020/10/19/combating-abuse-in-matrix-without-backdoors

There was a similar document shared on Secure Scuttlebutt ( #SSB ) / #Manyverse a while ago. I believe I linked the document, so search my history if you wish to compare.

Frankly, I found the SSB document unworkable and error-prone, but this one sounds like it could work in some situations.