Veronica8 I like how you used social media as an analogy, very fitting.
Another note is why have a "pin" button for putting up reviews you like as well as a delete button? While pinning reviews is good for showing actually good reviews that are nice and that viewers might not see due to not looking at the last pages of reviews, I imagine an author could flush out the bad reviews "ethically" by just pinning. (I'm not sure how many can be pinned though.) Although this does seem to defeat the purpose of up-voting a review that was deemed good. With the 'negativity' of a delete button, there should be a down-vote button too.
In short, the pin and delete and lack of a down-vote button seem to suggest the perfect combination of ways to over-inflate novels. But oddly enough, I don't see this as necessary as the 1-star and 5-star spam seem to balance one another out pretty well. Or rather, the critical versus the high-praise reviews. I can't actually think of a novel where a review or handful of bad or critical reviews really affected the rating. At least, I consider anything above a 4 to be good and stay away from anything less than that.