That would require it to be controlled, really. People recommend certain books because they're good. Word of mouth advertising.

You can't just take word of mouth and automate it and productize it somehow. That kills its nature.

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.