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.
We received the book on time but i received the book which has missing pages, from pages 234 to 252, means complete one story is missing. And in parallel, 1# story "Ariette" is repeated. Bit disappointed with quality and felt ashamed, to whom i gifted that i brought a book which without checking & is not complete :-(