To calculate the overall star rating and percentage breakdown by star, we don’t use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyses reviews to verify trustworthiness.
I've just been trying to figure out how to contact the seller because I found a mostly blank page on p. 39 - and lo and behold, happening upon the reviews I see that at least one person already reported this problem - back in 2016! Obviously, the problem has not been resolved. If you are actually interested in reading this excellent book, I suggest a different version.