This would be really great by the way, if done properly! The biggest hurdles on the.. ahem, previous site was locating games I wanted to purchase, then estimating if they had been sold or not (if the sales thread was 5 months old..)
So besides trades, this should be implemented for selling and buying as well! Imagine everyone would have a list of titles they're willing to sell (or trade) and buy (or trade), including the conditions and asking price. If these lists would be linked to a maintained list of games such as the ones that existed on NA, I could instantly see what my buying options for a certain games are, or, for instance have a notification appear once the games on my want list become available.
I'mm still looking forward to how the sales, feedback and all will work on this site and this could be ground breaking feature for that.