tl;dr Reviews are the #1 way books get readers’ attention, and that drives sales for authors.
There are all kinds of studies using all kinds of algorithms about how word of mouth impacts book sales for the better. You can read those, if you care to, or you can take my word for it.
Back when we all lived in a slower, kinder world, people sat and chatted with each other, and they talked about what they were reading. Now, only the most devoted bibliophiles hang out in in-person book clubs (except pandemic, which has largely killed those); most of us are lucky if we meet our Goodreads Yearly Goal, snatched in moments here and there in the interstitial spaces of our crazy lives.
The online book review has replaced actual word of mouth almost entirely. Whether it’s on Amazon, Goodreads (which is owned by Amazon now, but still has separate reviews), in the Silent Book Club group on Facebook, or other places altogether, people are discovering what their friends recommend, and making recommendations of their own, online. So for any author, having readers leave reviews is literally the difference between make and break for any given title.
We provide authors with business cards and post cards of their titles, so they can hand out reminders to people, but even then, people recognize these, appropriately, as promotional materials, and therefore biased. Before people spend their entirely valuable time on a book, they want to know if it’s going to have been worth it, and they rely not on promotional materials, but on real people’s reviews, to make that judgement.
What that means, is that as an author or a publisher, you can spend all the money on marketing you want, and it won’t make as much of a difference as receiving a well-written review will. As a reader, your review has more power than the Press’s marketing dollars. And that should make you happy; it’s one of the only places in the great wheel of Capitalism where the power resides with the people.
So get out there and flex that power. If you’ve ever bought a title from a small press, leave a review of the title on every platform you feel comfortable using. Get in the habit of leaving reviews every time you finish a title, whether it’s small press or big. You’re doing good in the world by doing so, and that’s a worthy use of anyone’s time.