Medieval Europe had very little in the way of trade, but when it finally became feasible to trade on the seas again the merchant class sprang up rapidly and was just as quickly preyed upon by all the cast-offs of feudal farmsteads (I.E. extra sons who were not needed around the farm became brigands and mercenaries).
Brigands were so bad that every village in medieval Europe had walls. Merchants often moved from castle to castle as they traveled the very dangerous, decayed roads of the Roman Empire, which local lords did not feel inclined to patrol or repair.
In other words, if trade works anything like it did in real life with caravans or even single people with carts, we're going to need to set up warehouses in cities we trade with regularly, law speakers who can deal with that city in the case of problems, and "castles" along the roads which can be maintained by powerful warriors (knights), who are supplemented by the cities with coin or steel, land, whatever. Valuable goods in quantities that make it worth maintaining roads and safety.
Assuming there -is- a brigand problem, that trade is sufficiently stymied by them, and those who trade and those who benefit from traders are willing to part with goods or coin for the benefit of themselves and others.
As it stands, if trade becomes profitable and common, most people who go to trade in other towns will at least need hired guards or friends to travel with them and fight off the foxes, not to mention the monsters that will eventually be in play.