The player marketplace is a menu where players can sell multiple items, rather then equipment, rings and other items that are equip able.
The marketplace becomes available when a player reaches mastery rank 10.
To bring up the marketplace menu, press the U button on the keyboard. A new player will receive one of many selling slots, these slots can be used to sell your items that you do not need for flux, eyes, glim and etc
A player can easily make a large profit by buying and selling multiple items on the marketplace. This can be achieved easily by using only one selling slot, or using multiple to gain flux at a constant rate. A simple means of doing this is by farming Eyes Of Q'bthulhu