If you think there`s a stool, you wouldn`t deal with a vampire. Different commodities have different prices, and the income from trade depends on the amount of the resource you produce. You can negotiate with another group if they don`t have the resource you`re dealing with – otherwise they won`t be interested. Trade is an exchange of goods that you can generate in certain buildings (wood, iron, exotic animals, etc.). They waved the finger at diplomacy and also took trade routes.
They even took the boats and cars of the poor little diplomacy on the campaign map. This is just one more symptom of the larger problem called Total War Diplomacy, something that has shown very little love and attention since the birth of CA. I have seen that political groups with +200 connections oppose profitable trade for them and political groups with +5 relationships accept the same trade. The diplomatic system here is very veiled.
Nor have I ever seen evidence that more trade resources increase the likelihood that someone will agree to a trade deal. To check how much money you receive from trade with a political group, you need to drive the mouse over the trade agreement symbol next to the political group indicated in the diplomacy tab. The income you receive from the resource can be verified by navigating to the resource indicated in the Diplomacy tab with the mouse. Each resource you export provides a sum of money in each round.