There's a whole successful social network (Goodreads) built on people's desire to talk about books, frequently in the form of effusive praise. I think being able to trace the product to a single individual (e.g. a book's author) helps make it particularly appealing to leave that sort of feedback: we know it feels great to hear that someone values a thing you've created, and we like the idea of giving that pleasure to the creators of things we like.

I somehow doubt it's in the form of 5:1 ratio of effusive praise to questioning/criticism outside of the true top books there, and then to see this on a random ad where the OP swears he's not contacted anyone about the Show HN and yet all his "happy" "lurking" "customers" pop up with really sweet words within an hour is comical

I understand people are nice sometimes, but it's clearly not organic here.

And yet it's 100% organic here. I was few times on the HN frontpage with my blog (that links my book) so I was hoping some of my readers actually hang out here. I postponed Show HN a few months to get a few hundreds customers first. But that's it.

You don't have to believe me, but it's the truth.

If you’re just looking at the top reviews for a book it’s more questionable; they tend toward the extremes: enraptured encomiums about how beautiful and important and bold the book is, or insult-laden rants where the book is a whipping post for the reviewer to show off what a biting sense of humor they have.

I swear nothing was solicited. I just posted it myself and waited. No Twitter, no mailing lists, nada.