How do expressions of doubt affect trust in online reviews? Some previous studies find that people trust confident advisors more than doubtful advisors, whereas others find doubtful advisors are trusted more. We tested the effects of expressing doubt using Yelp data and in a controlled experiment: In Study 1, reviews from Yelp (N = 5.9 million) were coded using the Linguistic Inquiry Word Count (LIWC) software. Reviews with doubtful language were seen as more useful, and this result was robust when controlling for other psychological and linguistic variables. In Study 2, participants (N = 660) evaluated reviews with doubtful or confident conclusions; doubtful reviews were seen as more likely to be written by actual consumers. In both studies, the positive effects of doubt were stronger for positive (vs. negative) reviews, suggesting doubt mitigates concerns about fake positive reviews. The present study emphasizes the advantages of expressing doubt.