I've used the marketplace once, when I needed a comp helmet. I didn't have any luck, so I went through C grade with a D grade helmet. -I did find a few comp helmets on the market in game, but they were overpriced.
It's rare for WTBs for such highly overenchanted items with the sole exception of Homunkulus swords to be successful - try a hand at making your own, or, failing that, keep a close eye out in Giran.
I would say only 10%, or even less then that, even come to these boards, so, its rare that you can find someone WTB or WTS through the site when the majority just do it all in-game.
People should read the marketplace even if they dont really want to buy or sell something. The main reason that marketplace is abandoned is all of posts from each servers published in one brunch of the forum. Reading this info is mostly wasting your time.
I have used it without sucess as your post gets buried in less than 1 day. It would be a bit more useful if they would split the Market Place into servers. Like
Lionna- Marketplace
Bartz- Marketplace
ETC