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 actually really enjoyed this book. Maybe because I enjoyed the class I used it with. I didn't read through it all the time line for line. But there are some really good nuggets in this book in terms of laws and libel/copyright. Knowledge is power.