The L4 – Marketplace is like a Duty-Free Store. It’s ran by extension from the U.N.C.L.E.S. Council and acts somewhat like a central warehouse. This central-sector marketplace can set buy/sell pricing to help the overall economics of the sector.
Nations and factions are always encouraged to trade to and from one another, but in a pinch, you can (almost) always buy/sell to the Market.