The ability viewers have to contribute information to websites (i.e., user-generated content) is a defining feature of the participatory web. Building on warranting theory, this study examined how viewers’ evaluations of a target are more or less likely to be influenced by user-generated content. The results indicate that the more a target is perceived to be able to control the dissemination of user-generated reviews online, the less credence people place in those reviews when forming impressions of the target. In addition, the less people are confident that user-generated reviews are truly produced by third-party reviewers, the less people trust those reviews. The results provide novel support for warranting theory by illustrating how the warranting value of user-generated information can vary and thus differentially affect viewers’ evaluations of a target. The implications of the study’s results for warranting theory, online impression management, e-commerce, and future research are discussed.