Amazon calculates a product's star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers and factors that establish reviewer trustworthiness.
I liked this book better than 5 Sec rule book. This book is Mel robbins debut book so she had lot to prove. She tried to include everything in it, even 5 sec rule for which she authored another book later to better explain the principle. Simple straight forward book. Just go for it. Mel always teaches right stuff.