If several stores are running low on a particular item to sell and then the owners put the price up, there is then a demand for that product. Merchants from other areas seeking to exploit this will send caravans with these goods on them to the city, generating quests to defend the caravans, some might pass through PvP areas allowing both NPC and PC bandits to attack while others will not, to ensure that some of the caravans get to the town.
Whenever a caravan gets to the town, prices will go down due to increased supply, shopkeepers might try to exploit this by funding bandits to attack the caravans, and hiring PCs to attack them, while not preventing a player from making a caravan and making some cash.
Shops such as Harquenist?s smithy will produce goods on their own if some PC or NPC sells them the raw materials.