Thinking a bit further. If I report someone, the client could then check if someone I follow, follows the reported account, and offer me to send DMs with a heads-up (warning) message.
Do not follow nostr:npub1q3954hly5yfw7lmlgwrphd9d77575cxdurw6ahczyptnkxw3k98qxdqjss, it's an impersonator of nostr:npub1uescmd5krhrmj9rcura833xpke5eqzvcz5nxjw74ufeewf2sscxq4g7chm. I mention it because at least one person I know follows them instead of the real Paulo.
Do enough clients support reporting? And are we already highlighting reports when we look at profiles? When someone is considering pressing the follow button might be a good moment to check for reports, maybe even retroactively to reduce load. Something I need to look into for nostr:npub1z29uqk4xl4pp6qxrcvufx20nnn782zcrtkmvmtfwkruc80l4v20sr9heag (only shows reports a person has made, not reports made about them).
Discussion
I think sooner or later reports will be abused. There’s an impostor prevention section on nostr design, have you looked at that by any chance?
https://nostrdesign.org/docs/how-to/impostor-prevention/
This was first seen in Nostur by nostr:npub1n0sturny6w9zn2wwexju3m6asu7zh7jnv2jt2kx6tlmfhs7thq0qnflahe