Abstract: This paper considers the impact of reviewers on the sale of a product of unknown quality. Sales occur simultaneously after an initial review by an unbiased, pessimistic or optimistic reviewer and we examine the impact on sales in each case. We find that counter-intuitively a pessimistic reviewer is best for the firm's profits regardless of the quality of the product. An endorsement by such a pessimist provides an excellent signal of the product's quality, while consumers expect the reviewer to fail to endorse, so receiving no endorsement will not impact too heavily on the firm's expected profits. This asymmetric impact provides a strong explanation for the stylized fact that reviewers are often viewed as being very critical.