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.
Without doubt the best on kettlebells and peppered with delightful humour. Though, with so many brilliant videos to learn from books are almost obsolete. Nevertheless buy it, practice, then diligently read before sleeping - you will sleep well.