Online reviews have become increasingly popular as a way to judge the quality of various products and services. However, recent work demonstrates that the absence of reporting incentives leads to a biased set of reviews that may not reflect the true quality. In this paper, we investigate underlying factors that influence users when reporting feedback. In particular, we study both reporting incentives and reporting biases observed in a widely used review forum, the Tripadvisor Web site. We consider three sources of information: first, the numerical ratings left by the user for different aspects of quality; second, the textual comment accompanying a review; third, the patterns in the time sequence of reports. We first show that groups of users who discuss a certain feature at length are more likely to agree in their ratings. Second, we show that users are more motivated to give feedback when they perceive a greater risk involved in a transaction. Third, a user’s rating partly reflects the difference between true quality and prior expectation of quality, as inferred from previous reviews. We finally observe that because of these biases, when averaging review scores there are strong differences between the mean and the median. We speculate that the median may be a better way to summarize the ratings.