Trust on the internet is largely facilitated by reputation systems on centralized online platforms. How- ever reports of data breaches and privacy issues on such platforms are getting more frequent. We argue that only a decentralized trust system can enable a privacy-driven and fair future of the online economy. This requires a scalable system to record interactions and ensure the dissemination and consistency of records. We propose a mechanism that incentivizes agents to broadcast and verify each others interaction records. The underlying architecture is TrustChain, a pairwise ledger designed for scalable recording transactions. In TrustChain each node records their transactions on a personal ledger. We extend this ledger with the recording of block exchanges. By making past information exchanges transparent to other agents the knowledge state of each agent is public. This allows to discriminate based on the exchange behavior of agents. Also, it leads agents to verify potential part- ners as transactions with knowingly malicious users leads to proof-of-fraud. We formally analyze the recording of exchanges and show that free-riding nodes that do not exchange or verify can be detected. The results are confirmed with experiments on an open-source implementation that we provide.