Collaborative systems are growing in use and in popularity. The need to boost the methods concerning the interoperability is growing as well; therefore, trustworthy interactions of the different systems are a priority. The systems need to interact with users and other applications. The decision regarding with whom and how to interact with other users or applications depends on each application or system. In this paper, we focus on providing trust verdicts by evaluating the behaviors of different agents, making use of distributed network monitoring. This will provide trust management systems based on "soft trust" information regarding a trustee experience. We propose a formal distributed network monitoring approach to analyze the packets exchanged by the entities, in order to prove a system is acting in a trustworthy manner. Based on formal "trust properties", we analyze the systems' behaviors, then, we provide trust verdicts regarding those "trust properties". Furthermore, automatized testing is performed using a suite of tools we have developed, and finally, our methodology is applied to a real industrial DNS use case scenario