Trade in the World of Icengale, and that of its Northern half, Elagneci, is a multi-level system that primarily flows to and from one central location. The lowest level of trade is that which happens within a specific kingdom or smaller region, such as Th'krash or the Crescent League in the Perryn Island region. One such aspect of this would be supplies coming from a landlocked city and making its way down to the ports, or goods coming into a port and making their way to the interior.
The next level up from is regional, which is the trade that occurs within a specific region, such as coal from the Duchy of Steas making its way to the Principality of the Righteous and beyond, such has to Wellspring, Th'krash, and Tir Audel. Or it could be perry making its way from the interior of Perryn Island South to the Ridge Communities and then on to the Crescent League.
The next step up from that is inter-regional trade, which is goods traveling between major regions. Tthis could be coal from the Duchy of Steas making its way to the Belthurl Peninsula or perry making its way to the Golden Sea Basin. Along the borders this is mostly just locally produced goods, such as flour from the coastal farm belt region of the Golden Sea Basin being traded across the channel to Nrowl Island. For the much broader trading, this is usually luxury goods that are either unique to a specific region or are of unusually high quality. One example of this is the coal from the Duchy of Steas. It is an extremely efficient source of heat and as such it is a preferred combustible material for use in ship galleys. As such a good deal of it makes its way past the local border regions and winds up in ships sailing to far regions. Another is perry, fermented pear cider. Pears only grown on Perryn Island and aside from a couple very small groves it grows nowhere else in the world. As such it is a luxury item that is sold throughout all the regions.
At very top level there is the world travel. More than a lot of people may not have any idea that there is a completely different world on the other side of the Godspawn Mountains and the Vainen Glacier, but most know that all trade flows to and from the Vainen Sea. It is hear that many luxury goods wind up, destined for storage in warehouses and vaults until such a time as the Icen Channel opens up and traders from both sides scramble to make a profit. In Icengale it is very common to sell goods from Elagneci with the term "Beyond Vainen." To traders this means from the other side of the world, but to many it simply means the next region past the Vainen Sea.
For the most part the bulk of your traders operate in a very small area, at one or more of the first three levels of trade. Only those relatively few commonly referred to as "adventurer merchants" will travel across multiple regions, often traveling back and forth on smaller trips while making their way ever eastward or westward. They trade in bulk goods to "pay the bills" so to speak, all the while accumulating luxury goods close to their source so as to maximize their profits. Many of these wandering merchants will start at the Icen Channel after it closes, circumnavigate the world over the course of two years, and hopefully wind up back where they started shortly before the Channel opens up again. Profits for the local traders are more reliable, but for those few with the spirit and courage the dangers of being an adventurer merchant can yield great rewards, if they survive.
Generally speaking the bulk of all trade, both overland and on water, consists of local goods, because that is what is most in demand and in most regions will generate the most profit. A ship's hold full of barrels of flour is more likely to sell out than is a hold full of 25-g.p. bottles of rum. So the bulk of cargo is made up of everyday goods. But, the smart traders know to leave some room for the luxury goods, because in smaller numbers these will more often than not return a good profit. For example, a captain might take two less barrels of flour and instead fill that space with 3 cases of High Seas Rum. Those three cases will cost far more than those two barrels of flour but will yield 10 times the profit. The trick is know which luxury goods will sell where and for how much.
When it comes to trade the masters are the Ansar Knights, a religious order of Warrior- and Priestly-Merchants. They area based out of Castle City of Ansar and within the Golden Sea Basin they have an absolute monopoly on trade. Outsiders are not allowed to trade within their realm, but merchants can travel through their territory, under armed guard, for a nominal fee. Many merchants traveling through their region gladly pay this fee is it pretty much guarantees their safety.
While they may hold a strict monopoly of trade in their kingdom they are actually fair and just traders. Their contracts are iron-clad and representatives of the Ansars are often sought out to draft contracts between two parties. And fortunately for most Ansar Knights are never far away. While not exactly "adventurer merchants" many Ansar ships and overland caravans travel great distances, selling their on wares and those others. The primary reason for doing this is they like to keep abreast of everything that is going on in the world. People are fond of saying that if you go to Ansar and ask a Knight what soup was served at the Gibbering Tavern in Nug City on such and such a date, they would have an answer. This is obviously an exaggeration, but not much of one. No one knows why the Knights are obsessed with knowing what is going on in the world, just that they do.
If one looks closely at the Ansar Knights, they can partly answer that question. The Ansar Knights are followers of Greycen, the God of Law. One of their sworn duties is to uphold the law, be it their own or those of others, so long as the laws are just. In the early days of their founding they sent their members far and wide to study the laws of others, but also to help enforce local laws. When reports were sent back to the Senior Priests local goods were often sent along as gifts. Eventually the routes traveled by the Ansar messengers became trade routes for merchants, as those routes often had Ansar Knights traveling on them, and traveling with them was safer than traveling alone. Eventually they evolved into the organization they are today, operating trading posts/inns and traveling the world as merchants in their quest for knowledge.