I like the marketplace, and i have a few ideas on how to improve it. Buying herloom points made me think about this.
1.
Right now you can only offer 1 item and demand 1 item and gold. Increase the number of boxes for both seller and buyer and include gold box as offer.
For example: I want to be able to trade a +2 item for two +1 items without making several deals involving shoving gold back and forth with the item.
2.
Make it so you can trade privately between 4 eyes.
Reason 1: If i want to give a buddy of mine an heirloomed weapon or just some gold so he can buy some equipment this would be very useful. I wouldnt want to put a free item on the market *hoping* my friend picks it up in time (A matter on convenience since there are ways to circumvent, like having you friend put up a straw hat).
Reason 2: Makes it safer to trade heirloom points (You have to put some possibly weird offers on the market to make those trades back and forth).
I also like poophammers suggestions:
http://forum.c-rpg.net/index.php/topic,16497.msg235237.html#msg235237