Amazon calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.
Johanna Basford has been so generous in this book, teaching you her tips and tricks for drawing Inky Wonderlands. I have had so much fun learning to draw things I wouldn't have attempted before. It's brilliant.