I see there are a lot of "I have X weapon, and I want W, Y, or Z". Some put the items down in the marketplace, while some make a post in the forums.
I suggest that if you make a post in the forums, make the trade possible in the marketplace as well. Why? Well, for starters you might find someone who does not check the forums much. And maybe something like this happens (I've done it once with a +1 weapon).
I want a German Greatsword, and I have a Highland Claymore. There is no trade like this in the marketplace. But, someone gives a Danish Greatsword for a Highland, and there is another one who gives a German for this Danish!. Thus, you can swap your weapon, and all 3 players have obtained their items.
PD: Obviously you can use the forums to advertise your product, or try to bargain prices with someone. But if you know you want a X for Y or Z... trade, use the marketplace as well!