This research explores the effects of tentativeness in online product reviews on consumers' product attitude certainty and behavioral intentions. Drawing on salience theory, attribution theory, and work in attitude certainty, I predict that, when consumers who have seen positive reviews of a product are exposed to a tentative review, their attitude certainty and willingness to purchase is reduced. I also predict that consumer reactions differ depending on the expertise of the review source as well as the product experience of the consumer.I also address confidence in information completeness as the metacognitive mechanism that explains the tentative review effect. Specifically, I argue that consumers who see a tentative review are sensitized to potentially missing information, which reduces their attitude certainty and willingness to purchase.Our hypotheses are tested in a series of experiments which demonstrate that tentativeness reduces attitude certainty and willingness to purchase but that the effect is attenuated when the reviewer is a novice and when the consumer has a high level of product experience. Based on the findings, I discuss our contributions to theory and suggest practical steps that firms can take to mitigate the effects of tentative reviews. </p