Trade energy allows you to change the prices of items you sell to your Town Masters. You can receive a major amount of energy by giving discounts and spend it on raking the price up when you need it. The higher the level of the artifact, the more energy you can spend or gain when trading them. You will also receive 2 units of energy for each deal as a bonus. Upgrading the Market increases the maximum capacity of your trade energy bar.
Spending energy on trade allows you to earn more gold than simply fulfilling your Masters’ requests, and much more than simply selling them from your inventory.