Goods drift from where they are cheap toward where they are dear. Move them faster than they drift, and keep the difference.
Goods drift across the realm on their own, flowing from where they are cheap toward where they are dear. Every point on the map has a price for every good. You run wagons that move goods far faster than they drift, pocketing the difference in price between pick-up and drop-off. Sell a lot in one place and the price there falls; buy a lot and it rises.
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