5G networks intend to cover user demands through multi-party collaborations in a secure and trustworthy manner. To this end, marketplaces play a pivotal role as enablers for network service consumers and infrastructure providers to offer, negotiate, and purchase 5G resources and services. Nevertheless, marketplaces often do not ensure trustworthy networking by analyzing the security and trust of their members and offers. This paper presents a security and trust framework to enable the selection of reliable third-party providers based on their history and reputation. In addition, it also introduces a reward and punishment mechanism to continuously update trust scores according to security events. Finally, we showcase a real use case in which the security and trust framework is being applied.