Trade is how a settlement pays for everything it can't produce, but it punishes breadth. Sell two or three goods heavily rather than six or seven lightly. A trading post spread across many goods becomes hopelessly inefficient. Worse, every new export route costs coin to open, and the price climbs the more routes you already run.
Process before you sell. Raw resources are worth a fraction of their finished form. Ore sells for roughly a third of what the tools made from it fetch, so exporting raw ore is barely worth the trip. The same logic makes sidearms a better use of iron than mail armour, since they cost half the slabs for a comparable price.
Importing food is how treasuries die, with one exception: wheat bought cheaply, baked into bread and sold on turns a real profit. Imports are for one-off needs, stone for a church or iron for an armoury, not monthly survival.
Bartering through pack stations sidesteps trade posts, but it has no send limits, so never barter anything critical. Honey, wax, pelts and hides are safe because running them to zero costs you nothing. Food is not, because an empty stock is a starving town.
Trade & Wealth
Trade post gets hopelessly inefficient, and route-opening costs tank your treasury early.
Import at 12g, bake it, sell bread at 5g each. Fruits or meats on constant import will bankrupt you.
Observed trading-post values scale roughly 1:2:3 from ore to slab to finished tools. Selling raw ore is barely worth the trip.

Once it's fully staffed and horsed, more horses add nothing. Build a second trading post to keep scaling volume.
Early routes can unlock for well under 50 coin; later ones run several hundred. Budget for it instead of assuming routes are free.
Opening a route costs gold, and spending the starting purse on anything else strands your first exportable good with nowhere to sell it.
Read all 13 Trade & Wealth tips in the field book →
Bartering (Pack Stations)
It's powerful (doesn't tie up trade posts), but a food that hits zero = starvation.
Barley-for-pears left one region with rotting fruit while home ran dry; ale-for-barley ran out for months yearly. Until send limits exist, don't build your food economy on it.

Save barter for non-consumables: stone for castles, iron for armories.

Read all 8 Bartering (Pack Stations) tips in the field book →
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Warfare & Militia
Regional wealth is what buys mercenaries before a contested region, rather than after.