Amazon calculates a product's star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.
I was very happy with this machine until the point where I had to empty the waste canister. It got stuck together and won't come off. It is really the only drawback, I wish they made this part easier to maneuver. I had to return the item back because the canister will not separate.