This is what I subtly questioned: How do you want to know if it's real word of mouth or growth hacking?

I've bought lots of books through HN recommendations, more often than not they're great. I do always check a bit of the poster's submission/comment history though, because people definitely do try to pitch their eBook or SaaS here.

I bought Deep Work off a HN recommendation, that included a whole bunch of follow-on comments about how great it was.

And it was well worth it.

I cannot imagine the author of this book resorting to growth hacking.