The city of commerce built its wealth on four major factors. One is the freetrade agreement with the thaian kingdom to which they in theory belong. This ensures trade with all cities, cultures and lands, known or yet to be discovered. Often seen as a separate law but actually part of the free trade agreement is the gambling licence, that is unique in the Thaian Kingdom, because 'commercial' gambling is outlawed since the times of king Yorik I.
Another factor is the shipping dock and the woodcutting in the Venore area. Before the Edron colony was established, the Venore area was the major source for wood needed for constrution and tools. What seems odd at the first glance, given the swamp area Venore was built in becomes more understandable when considering the next factor: Until the Druids and mages drove away all those poisonous insects and creatures the area was known for its diseases and a criminal colony in the beginning. So the merchants had a steady supply of cheap workers that had to do every job appointed to.
The last factor was the discovery of the Spiceweed. A special swamp grass that was soon used by cooks and households all over the continent.
Soon enough the merchants became rich and powerfull, rivaling most of Thais noble families in wealth and power.
For now the merchants seem content with their station and the place Venore takes on the continent and in the kingdom. There are voices that Venore might separate one day or use it influence to wrest even more rights and privileges from the kingdom that becomes more and more dependent on its economical power.