Why would anyone engage in risky business with a total stranger? In this project, we analyze how criminals cooperate on Dark Web forums. We use rational choice and game theoretical explanations of individual trust and study effects of reputation, information diffusion and rule enforcement on exchanges in Dark Web criminal networks. We use text mining techniques, advanced social network analysis and agent-based models on unique longitudinal data of online exchanges from more than 13,000 Tor forum hosts to answer our research question.