On the left (on your side), the interface shows you how much you earn with the trade and resources you export to your trading partner. The right side shows how much money they earn and what resources you import from them. The only unit belonging to European merchants is the Black Ship, the most powerful naval unit in the game. This ship appears on its own and sails along the west and north coast of the map. If the black ship is captured by a clan, European merchants will not make other ships unless the original ship is sunk. Attacking and/or firing at the merchant ship does not irritate traders, and cannon weapons can still be purchased. The price of commercial goods is influenced by supply. With too many merchant ships on knots that produce some kind of good flooding in the market to bring down prices. On the other hand, too few ships would not be able to produce enough cargo to meet sufficient demand. As more ships produce more resources on a node, they produce fewer and fewer resources per ship. A balance can be found fairly easily by adding or subtracting ships from commercial nodes one by one until the income is maximized. As a general rule, each node can support about five vessels. Commercial goods can also be produced by plantations.
Some goods are only manufactured in certain regions. Tea, for example, is only available in India. Ivory cannot be purchased on plantations and is only available through commercial nodes, so powerful maritime fractions can easily create a monopoly. I have never seen evidence that more commercial resources would increase the likelihood of someone agreeing to a trade agreement. The diplomatic system is very veiled here. I have seen that groups with 200-plus relationships are opposed to profitable trade for them and that groups with 5-strong relationships accept the same trade. As in previous total war games, the trade routes of enemy nations can be plundered for money. The amount of money earned depends on the number of ships invading the route and the value of the trade that takes the route; If you move the cursor by route, it is indicated how many of each of them. The amount earned is generally not significant, but it is the most useful way to occupy otherwise inactive vessels and can help offset their maintenance costs somewhat.