well 90% of trading are fg to AD (astral diamonds) most valued currency on NW, you can use it to many things.
If i am selling 1m ad to you for X fg, YOU post item in the neverwinter AH (auction house, cause its the only way to transfer AD btw other accounts in this game, and there is a 10% cut)
So you post random item for 1.111.111 at AH, tell the seller your item's name, you send him fg and he buys ur item.
Simple, but it seems there are no many sellers atm, and price on AD:FG changes too much. Its a bit hard to farm AD on NW thats why.
Cheers