If I can find similar tastes, maybe a little bit different, then that will result in good recommendations.
So I would want to find people who both like similar things but also dislike similar things. It will be interesting to find people my similarity and see which are best at finding books I like.
That's one of the problems I have with ML-based recommenders. I can't identify any particular ML algorithm, and therefore I can't say "This one has consistently given me bad recommendations, so I'll ignore it. But I do like this one over here." Whereas with my friends, I know that Lori and Nicole gives good recs and Brad doesn't, so I'll ignore Brad's and read recs from the other two.
Or the thought that such things, if not happening, may happen? Just like on Amazon and other sites?
In particular, I'd like to see an engine take a reviewer's dislikes into account more. If someone likes (switching to film for an accessible example) Cinderella, The Little Mermaid and Mulan, their opinion on Brave isn't going to carry much information as they're pretty indiscriminate about Disney films. But if they love Mulan, dislike Little Mermaid and hate Cinderella, their opinion on Brave is more likely to line up with my own.