Some of my favorite npubs are bots. For instance nostr:nprofile1qy88wumn8ghj7mn0wvhxcmmv9uq36amnwvaz7tmwdaehgu3wvf5hgcm0d9hx2u3wwdhkx6tpdshsqgqudjezn946405jr0x5tj9kyyajm2cfd7ywfwjk0r2r6x26rp592ylzagql and my feed of news bots. There are definitely several bots around that can be considered useful or entertaining.

Additionally, as far as the protocol is concerned, any post is considered legitimate when it is signed by a private key. There is not a way, at the protocol level, to distinguish between a private key controlled by person, and one controlled by a bot.

That said, there are ways to generally keep bots out of your feed. First, use paid relays or web-of-trust (WoT) relays. In particular, use these for your INBOX relays. That is, the relays where you will be reading from for anyone trying to tag you or DM you.