The Trading system came to be due to the first campaign I have held in this setting. The players and I decided as a group they wanted to play Burning Wheel characters that were building up a trading company.
Thus a system was required to figure out how to trade and what type of goods they could expect, with the system of resources as a tool to figure it out. Towns & Cities have due to this a trading table aswell with a Hidden GM table with some more exotic (or not so very legal) goods. Something the players have to discover over time through the game. And also a table with exange rates for the towns.
The Trading system has two major pillars.