Added with the update of 28 June 2012, the Galactic Trade Center (GTC) allows you to do a limited amount of in-game trading, useful for those players who don't normally trade, are not in a legion, or have an excess of Artifacts that either can't be used, or don't get used often enough.
Due to the nature of the GTC, prices may not be equal, or even close to the Artifacts current value in the open market, through forum posts or trading groups on Facebook, both of which also deal exclusively in Complex Tech Parts (CTP) or Kurinite (Ku) as exchange currencies, sometimes also in Exotic Matter (EM), but just about never in Credits (Cr).
Currently you may only bid on 2 (two) items at a time, same goes for selling items lots (where a lot is 1 or more of the same artifact). Prices are in Credits (Cr). More bid slots and auction slots are available for 25GP (Galaxy Points), which must be bought with Facebook Credits, or earned from surveys, etc.
If you would like to sell your artifacts in volume for CTP or Ku instead of Cr used by the GTC, with the freedom to sell or buy more than 2 item lots at a time, then The Trading Post on the Forum, and the Facebook Group, The Trading Post Second Floor are a good place to start.