Here to teach you the ways of the trade in Eiyuden Chronicle: Hundred Heroes is Hogan. By the time you can add him to the Alliance, you'll be a master in trading goods.
On the dock in the west side of Twinhorne West you'll see a lizard man, Hogan. When you talk to him he will tell you that he will join when you've made 50,000 Baqua via trading. We did this by fast traveling to all areas with trading posts marked on the map (labeled with a balancing scale icon) and noting the top 3 highest income items you can sell and noting how much they sell some of the top items for. These were mostly diamonds, paintings, and carvings but will depend on what your trade market is doing when you get there, as that changes regularly in the game.
Buy these items from the cheapest locations and sell at the most profitable and you should be able to climb up to 50,000 Baqua fairly quickly assuming you start off with a decent amount. Once you think you've made it to 50,000 speak to him again and he will be recruited into the Alliance.
It stands to reason that once you've mastered trading, Hogan comes into your town and runs trading there as soon as you build the Trading Center at the Drafting Studio.