I've lately been gathering data using a circuit method (mimics standard addition [chemistry] making each good cycle by the same amount of days) and developing a matrix of production verse use to identify trade partnerships.

What I've found so far, (over half a day in of analysis mind you) is that while the games premise is that production necessitates trade in a rock papers scissors affair the reality is quite different.
The key goods to steam roll capitalization in Patrician 3 is Beer, Iron Goods, Salt & Wine; with obviously Iron Goods & Wine being the most profitable by margin span.
This is unilateral across the Hanse, the sheer amount consumed dwarfs everything else and while not everywhere are good producers, those producers are quite imbalanced as the only main real source of profit.

Now i hear you say what about captains on auto trade and hiring an administrator.
These two things still don't change the fact that the daily profit margin increment is favored towards those same 4 high consumption goods (that most importantly don't vary from town to town) and that the profits generated by use of these methods does not make the trade of any other good truly any more viable because you would end up needing information on days travel to mesh with the good cycle.
I mean if your buying at the absolute lowest price of course you will make a profit, but it won't be an efficient turn of profit in the least.

Is it just me or the whole premise of trade in this game seems to boil down to the designer having a massive balance design fault of trade centers that are not equidistant (in fact rather erratic) and then trying to patch up the balance with the rock papers scissors style goods trading that is then undermined by the fact the city level of the trade simulation doesn't seem to utilize to any great measure the afore mentioned rock paper scissors trade good products.
Made me laugh when i made the analogy that every single Hanseatic town was having it's population mummified (salt) and replaced with bioethanol fueled mechanoids (beer/wine & Iron goods).
I mean they don't even seem to want food :P all that much (though arguably a good way from playing to generate a profit by margin).

There are quite a lot of people out there bragging about massive trade fleets and millions of dollars etc., but it feels as though at some point the game moves away from it's idea of conquest by trade; into conquest by padded automation cop outs.
I mean you COULD put a ship in every city and monitor all changes for the sweet spots of production verse consumption; but when you only need to sit on 2 maybe 3 cities (out of the 24) to garner the lowest price and everywhere wants to give you mad bucks for your 2-4 items; i feel it becomes more of a butter churning simulator rather than a trading one.
Sit in city pump & out good, throw at hanseatic wall; rake in mad bucks.
Ah well at least THAT is still better than Patrician IV Conquest by Fire (burning towns to the ground to own business/ garnished with the obscenely profitable turnaround of piracy).

Still it's looking like all these trade games have one thing in common... shit half arsed trading systems.