The Aztec markets were barely regulated by the government. Trade and tribute were critical to the city of Tenochtitlan. One fourth of its food came from tribute it imposed on conquered city-states.
The Aztec economy was technically a barter system but there were two unofficial currencies: cotton textiles and cacao beans, the main ingridient of chocolate. They grew in the tropics of south Mesoamerica. Cacao beans were used to make a hot chocolate like drink, which, due to its cost, was only drank by nobles. Deceptive merchants sometimes produced counterfeit cacao beans.
The Aztecs conducted trade with their primary enemy, the Tarascan Empire. The Aztecs sold them obsidian. They were the Aztecs' only source for bronze and copper goods (http://www.public.asu.edu/~mesmith9/MES-05-SciAm-.pdf P97). Obsidian blades were used in everyday life by virtually all workers. They were used as razors, sickles, scrapers, drills, arrow heads, and knives, which were the most common. Obsidian blades are incredibly sharp. The Aztecs got most of their obsidian from Otumba and Pachuca. The obsidian from Pachuca has a green tint and was harder than other obsidian. There was also a complex system of ceramic exchange. There were multiple centers of production for ceramics. One of these centers of production was located at or near Tenochtitlan.
There were two types of merchants in Aztec society: regional merchants and international guild merchants. The international merchants were organized into guilds whose membership was hereditary. These guilds organized large trade expeditions where they, along with professional carriers, went to various markets where they bought and sold goods. They were allowed to conduct trade in enemy states. They traded mainly luxury goods and, despite the fact that they accumulated large amounts of wealth, they were unable to become nobles. Regional merchants sold mainly utilitarian goods.