User reviews have become a popular source to assess the quality of products in consumers' purchasing decision. New insights into the effect of user reviews on product sales can be derived from examining review credibility and author popularity in our example of book sales from Amazon.com. We found that (1) average rating of reviews and diversity of ratings positively affect book sales, but (2) high diversity weakens the effect to sales, showing a quadratic effect of diversity on sales. In addition, our results suggest evidence that (3) review credibility and author popularity moderate the positive association of average rating of reviews and diversity of ratings on sales. Finally, (4) consumers seem to pay more attention to reviews for digital books than for paper books.
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