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.
So it's Easter morning and my daughter asks me why there are random stickers throughout her brand new book from the Easter bunny. I look inside and there is a half empty sticker sheet. When it showed up with a greasy cover I guess I should have inspected it further. Highly disappointed.