This paper investigates the prevalence and market conditions that encourage or discourage promotional reviews in the context of online hotel reviews. The authors, Dina Mayzlin, Yaniv Dover, and Judith A. Chevalier, use a differences-in-differences approach to compare reviews on two travel websites: Expedia.com and TripAdvisor.com. Expedia allows reviews only from users who have booked a hotel through the site, while TripAdvisor allows anyone to post reviews. The study examines the distribution of reviews for hotels on both sites, focusing on the impact of hotel characteristics and market conditions. Key findings include: 1. **Incentives for Review Manipulation**: Hotels with nearby competitors are more likely to receive negative fake reviews on TripAdvisor compared to Expedia. 2. **Hotel Ownership and Affiliation**: Independent hotels, owned by single-unit owners, are more likely to engage in review manipulation than branded chain hotels owned by multi-unit owners. 3. **Management Structure**: Hotels managed by small management companies are more likely to engage in review manipulation than those managed by large management companies. The authors argue that the cost of review manipulation, which is related to reputational risk, determines the amount of manipulation in equilibrium. They also consider the impact of hotel neighbors and their characteristics on review manipulation. The study uses a rich dataset of hotel reviews and controls for various observable characteristics to robustly test these hypotheses. The results suggest that the design of travel review sites and market conditions significantly influence the extent of promotional reviewing activity.This paper investigates the prevalence and market conditions that encourage or discourage promotional reviews in the context of online hotel reviews. The authors, Dina Mayzlin, Yaniv Dover, and Judith A. Chevalier, use a differences-in-differences approach to compare reviews on two travel websites: Expedia.com and TripAdvisor.com. Expedia allows reviews only from users who have booked a hotel through the site, while TripAdvisor allows anyone to post reviews. The study examines the distribution of reviews for hotels on both sites, focusing on the impact of hotel characteristics and market conditions. Key findings include: 1. **Incentives for Review Manipulation**: Hotels with nearby competitors are more likely to receive negative fake reviews on TripAdvisor compared to Expedia. 2. **Hotel Ownership and Affiliation**: Independent hotels, owned by single-unit owners, are more likely to engage in review manipulation than branded chain hotels owned by multi-unit owners. 3. **Management Structure**: Hotels managed by small management companies are more likely to engage in review manipulation than those managed by large management companies. The authors argue that the cost of review manipulation, which is related to reputational risk, determines the amount of manipulation in equilibrium. They also consider the impact of hotel neighbors and their characteristics on review manipulation. The study uses a rich dataset of hotel reviews and controls for various observable characteristics to robustly test these hypotheses. The results suggest that the design of travel review sites and market conditions significantly influence the extent of promotional reviewing activity.