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.
The printing quality of the book is not good, everything is blurred. Also the paper quality is not good, so while reading you see the black lines from the backside of the page. Adding too much stress while trying to read this book