The fast-growing platform economy has raised various economic and policy questions. This study focuses on two issues that have attracted a lot of attention recently―online reputation system and data concentration. A unique dataset is collected on hotel reviews from 4 major online travel agencies (Agoda, Booking.com, Expedia, Hotels.com) and TripAdvisor through web crawling. The empirical results cast doubt on the effectiveness of online reputation systems that reduce information asymmetry and build trust among users in the platform economy. Further, it is shown that the incentive for platforms to correct for information asymmetry may not be sufficient. We then reviewed recent discussions about the potential economic harms of data concentration. Platforms may acquire and abuse market dominance based on big data. The possibility that collusion is formed/facilitated through algorithm utilizing big data triggers a discussion of whether the current cartel policy is still valid. Finally, privacy infringement is critical to all of these data concentration issues.