Online platform-based marketplaces are central to our internet experience, but they present unique challenges compared to traditional stores. A key issue is ensuring trust between buyers and sellers without physical product inspection. My research explores how platform policies influence consumer choices using big data. I apply advanced techniques like causal inference, econometrics, and natural language processing to analyze data from e-commerce clickstreams and user-generated content on platforms like Reddit and Goodreads. By identifying patterns, my work aims to enhance trust and efficiency in online marketplaces for all users.