Online communities provide a social sphere for people to share information and knowledge. While information sharing is becoming a ubiquitous online phenomenon, how to ensure information quality or induce quality content remains a challenge because of the anonymity of commentators. This paper introduces moderation into reputation systems. We show that moderation directly affects strategic commentators' incentive to generate useful information, and moderation is generally desirable to improve information quality. We find that when being moderated with different probabilities based on their reputations, commentators might display a pattern of reputation oscillation, in which they generate useful content to build up high reputation and then exploit their reputation. As a result, the expected performance from high-reputation commentators can be inferior to that from low-reputation commentators (reverse reputation). We then investigate the optimal moderation resource allocation and conclude that the seemingly abnormal reverse reputation could arise as an optimal result. Our study underscores the importance of moderation and highlights that the frequency of moderation should be properly chosen for better performance of online communities.