When trade cities are under siege you can still trade with it. If the siege is relieved and the original owner maintains control you will trade under his trade rules, if the city falls to a new owner you can still trade with it under the new owner’s trade rules. If a new owner doesn’t post any trade rules (eg tax rates and bans) in their orders there will be no taxes. If the city remains under siege no trade will take place unless both the attacker and defender say to allow it (in their orders).
