Liberating the Market unlocks trade with your citizens. Once you complete that mission, you will be able to see the trade energy indicator, and citizens will start asking you to sell artifacts.

Trade energy allows you to change sale prices. 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 artiact in question, the more energy you will spend or gain trading it. Additionally, you get a small amount of energy with each deal. Trade allows you to earn more gold that simply fulfilling your Masters’ requests, and much more than simply selling them from your inventory.

Still, if you need some gold right away and you have a lot of crated artifacts but your Masters don’t make a lot of requests, you can akways sell the items straight from the inventory, albeit at less profitable prices.