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 bought 2 packs together - total 8 markers. Only 3 worked properly. Other 5 did not. Vendor is fooling people by reduction prices with low quality and defective product. Was not able to write at all with 3 markers. 2 markers work for very little time. However 3 were good. By the time I broke the package and did not get a chance to return.