This dissertation investigates various aspects of economic interactions in the digital age, comprising three papers that explore network supervision and coalition formation, price signaling and reputation building on online platforms, and the effect of online business on offline stores. The first paper examines the conditions under which collusion may or may not occur among agents when a principal cannot directly punish or reward them, focusing on the role of communication networks in limiting collusion. It introduces a novel algorithm for calculating agents' bargaining power and characterizes an optimal communication network that minimizes agents' bargaining power. This paper contributes to the understanding of various contexts, including anti-corruption, anti-trust, firm management, and political bargaining. The second paper investigates the relationship between price signaling, review-based reputation systems, and firm quality on online platforms. It presents empirical evidence from the service platform Zaihang, showing that high-quality firms adopt low introductory prices and supports the model's predictions on price and sales dynamics. The findings suggest that platforms can accelerate quality revelation by facilitating price signaling. The third paper analyzes the impact of online stores on brick-and-mortar (B&M) stores, using a unique dataset from a shopping mall to explore the positive and negative effects of e-commerce on different store types. The results highlight the heterogeneous impacts of online sales on various industries and provide managerial suggestions for B&M store and shopping mall managers, shedding light on the complex relationship between online and offline sales in the digital age.