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.
Excellent but not easy read! Aurobindo's work, be it Essays on the Gita, or Isha Upanishad, is no easy read. But it is "hardcore" philosophy, and if you dare to enter there, you will be rewarded with a changed outlook towards life.