Migdard's economy is primarily driven by adventurers, who tend to buy and sell items far more frequently than average citizens.
In addition, the Leika Organization has some unique currencies that can only be used for purchases with members of the organization. See the Leika Organization currencies guide for more information on these.
The prospect of making money from seemingly nothing can be daunting to many adventurers. Most adventurers will rummage through their inventory and believe that most of what they've gathered in the fields is useless junk that isn't really worth much.
Citizens, such as various merchants and vendors, will be more than happy to take such items off of adventurers' hands, giving Zeny in exchange.
A wise adventurer, however, holds onto more valuable items because they know that other adventurers will pay more Zeny than the vendors in town for things like equipment, cards, consumables, and items that are needed for quests or skills.
As the population of Midgard increased over time, naturally, so too did the various stores. Soon, adventurers and citizens alike started complaining that in many of the larger cities, one could hardly take a step without nearly bumping into a store and that merchants have gotten more ridiculous with the placement of their stalls. In an effort to combat this congestion of the city streets, King Tristan Gaebolg has decreed that any merchant who wishes to set up a vending or buying stall must do so in the Marketplace.
Some adventurers--Namely Merchants and Super Novices-- have decided that selling their possessions to other adventurers is the way to go when it comes to making more money and have devised means to do so. With their Pushcart equipped, such adventurers can open up their own market stalls and sell their wares. The more research they invest in market affairs, the more items they can sell at once.
While adventurers can sell things to other adventurers for great prices, they can also set up their stalls to buy goods from other adventurers. Merchants can Open a buying store while non-merchant adventurers can purchase and use a Black Market Buyer Shop License for 500z from the Black Marketeer in Morroc at the pub.