(Names and most specifics have been wiped, just cuz I don't want things to get worse):
1. A Reviewer posted a bad review of the Author's book on a popular book site.
2. In the comments, Reviewer picked out a couple users who liked the book (and had little or no other activity on their accounts), suggesting these accounts were sock puppets -- created by the author to artificially boost the book's rating.
3. Reviewer's readers agreed and mocked Author for such "obvious" fake accounts.

Oops. Moving on . . .
4. Author left a comment in the review thread -- not to comment on the review itself, but to mention that none of the accounts were fake (one of the accounts was actually her daughter).
5. Author was told somewhat bitterly that Reviewer is entitled to write whatever she wants about the book (note again, though: Author said nothing about the review).
6. A couple of people who liked the book spoke up in Author's favor (some in the thread, some in their own reviews).
7. These people were accused of being trolls, sock puppets, or both.
Then things got worse.
Friends of Reviewers left multiple 1-star reviews after not reading the book. Hateful comments were left on the reviews of the "fake" accounts. At one point, Author thanked a different reviewer for reading the whole book and being impartial, at which point two commenters blasted her for "dictating" what makes a review fair or not.
It's like this particular group of people has experienced other authors acting badly and assume Author is doing the same thing. They've seen authors with fake accounts and assume that any suspicious account is, likewise, fake.
To user-reviewers then: This is not (always) the Bad Author you're looking for. Sometimes people mean what they say, with no other agenda. Best not to assume.
But this whole thing just proves to me why commenting on bad reviews -- or trying to prove anything on the internet at all -- is generally a bad idea. Authors, don't comment on negative reviews. Yes, there are thousands of user-reviewers who will act professionally, even toward authors whose books they don't like. But it's not worth risking the ire of those who will misinterpret everything you do.
Professor Internet is right: it's better to just chill out and eat a sandwich.
What do you think? Would you have stayed out of it? (I don't know if I would have). Is there a way to step into this without making things worse?