This work introduces a multiagent model for informal communication about cheating merchants among investing Genoese traders in the 12th century. The model builds on previous, game theory focused work of Avner Greif and extends it by enabling communication between Genoese traders. A trust-based cooperation model is tested across different network topologies as well as two different communication modes: (a) a reactive one representing Genoese trader interrelations and (b) a more proactive one that is based on accounts on the relationships among a North African traders collective, known as the medieval Maghribi Traders. The simulation shows that even for high levels of initial trust among Genoese, their mode of communication would not have sufficed to collectively identify cheating merchants and prevent them from future transactions. The results obtained from the tested network topologies are further discussed in the light of literature accounts of both historical societies.