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 have had nothing but good luck with the Kindle products and the Amazon service is top-notch they have taken care of every issue immediately. The only real issue was my own stupidity I accidentally logged in with two different accounts. When trying to sync my devices they got a little confused LOL I called and the extra account was deleted and I was given my Kindle 10, (I had purchased three days earlier) at the customer appreciation price $119 my account was fixed and I saved $30! AMAZON PRIME ROCKS!