On Amazon, when the system associates a product review with a product purchase, that review is from a "verified purchaser". Reviews from a verified purchase tend to be reliable (please see the next question below), since Amazon has already confirmed an actual purchase of the product being reviewed.
On the flip side, if an Amazon review is not from a “verified purchaser” there is no way of knowing for sure if the reviewer purchased or even used the product. While it is possible that a reviewer could have purchased the product elsewhere and left a review on Amazon at a later date, without purchase verification, it is impossible to tell. In our opinion, dishonesty is likely when an Amazon review is not associated with a verified purchase