Irishfast said that, the longer the trip, the higher the income. It is not obvious to me. Play a Lakota and set far away cities, the first caravan will also bring you 20 wealth (COM1).
Irishfast and Master Silver say that there is nothing you can do about rerouting a caravan. It seems so. But they do themselves. Building City 4 on a new continent, most or all caravans went to this city (so they got killed by sloops on the way). Could it be avoided? What is then the point in having the special golden icon to use with your caravans?
It seems that, when you have more cities, caravans do longer trip involving several cities –maybe all, but only some parts are remunerated? This point and the one before could have a significant influence on your economy if you have a widespread network of cities, compared to a cluster where they are as close as possible to each other. Or a very remote city where the caravans have to make a very long trip (Mesa map with one backyard entry, Continent far away, city on top of a high slope, surrounded with rivers).
For every COM science, each caravan trip brings you 10 wealth more. The evidence is the Nubian. You can have a caravan without any COM. This first caravan without COM1 will bring you 10 wealth, what no other nation does.
If you are Nubian, you get a +20/-20 discount on prices. But the Nubian cannot cumulate with the +10/-10 bonus on the corresponding rare. I moved, killed my merchant there, the prices did not change at all.
Master Silver says: the price of goods is influenced by the way you and other nations buy and sale. Sure, but not only. If you are the only Nubian, at Ancient, prices start to fluctuate since the very beginning of the game, when nobody has purchased anything. It seems to me that prices fluctuate according to the stocks of the warehouses of all nations put together, like in real life:
I want to buy timber (at Ancient, Nubian), price going down from 105 to 101. I save the game at 101, I build barracks but do not buy. Price for timber jumps at once to 123 and increases, but not for long. I reload, do not build barracks, prices goes down to 99.
Do you have more ideas about the statistical model about trade?