You can learn all this info in game, by doing trading, using the asses good deals option in the marketplace of the towns, using the Merchant's Ledger, talking to the guild master about trade and production of the different cities, so consider the information below.

The tips and informations originate from Tale Worlds Forum and are just summarized here. You also learn an example trade route that goes around all Calradia in Warband. In this article, you learn example price ranges and thresholds (to buy under X, to sell over Y) for the most profitable goods.

Trading goods is a great way to make money in Mount & Blade: Warband.