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 imagine if I'd read this book when it first came out, then I'd have been bowled over. However, many of the tools in here feel obvious in 2020 and not particularly surprising. That's not to say there aren't some nuggets of gold in this - I have possibly read too much behavioural science to be truly wowed.