Spam prevention should work by discarding events from users that are not connected to your social network like normal users are. For example, swarms of users that are connected by only 1 or less follows from legit users.

Iris already discards messages from completely unconnected users, but need to add shared block list support and better detection of sybil swarms.

This should work especially for trending algorithms, where reactions from socially connected users are more valuable anyway, and missing a like doesn't matter so much.

Currently Iris trending list comes from nostr.band, but I want to do it locally at some point. That's the only way you know what you get.