only "official" books that were written by the author would come accompanied with a token that verifies it; to side-step marketplaces (at least on physical copies), publishers could embedded an NFC chip into the book, consumer taps it with their phone to auth it; token also gets access to special discord, early release of author's next book, etc

I think even without an NFC it's clear that it's not a real book as soon as you buy it. But it's still garbage, and it'll still be impersonating the author, making it look like they sell garbage.

How does one validate that the NFT was issued by the real author and not a scammer issuing NFTs in the same name?

Via a 3rd party NFT minting service. In order to create the NFTs the original author could set up an account with the 3rd party, KYC herself and then mint tokens for every book she sells. 3rd party verifies/authenticates the book + NFT

How does the book purchaser verify the third party NFT minting service verified the NFT was created by the author and not some skammer using the same name?