Cheezy trade exploit:

[myz]

well, it could be interpreted as the medieval mafia, so if the neighboring nations' merchants do not pay protection money (pay in terms of losing trade $ every turn), your agents (of the mafia) will not let him conduct business, easy as that. Your own merchants bring in trade money for you every single turn they are on the resource, so consider that as protection money paid, so he can do his thing. Don't tell me there is no bribery involved, I mean, the pope is on your (and potentially other factions') payroll, right? It's natural for you to be on the merchants' payroll. Whoever don't pay, he can't trade.