When a trade is complete with the buyer/Seller, go to your thread and copy the URL, it will be something like (http://forums.gwonline.net/showthread.php?t=427749). Click the trade rank link on the left next to the username in the trade post and you will be taken to their forums trader page.
Click the Feedback for Username Link
Select if you were the buyer or seller
Select the 'Overall trading' experience (Positive, Neutral, Negative)
Add a short comment
Paste in the URL of the thread where the trade originated (should be in your clipboard if you copied it)
Add additional comments if you wish.
Your feedback has now been left in that user's profile.
The User you concluded the deal with will then be sent a PM saying you have provided feedback and they can reciprocate and leave you feedback.
Note this is not tied to your traders.gwonline.net account, this is for forum traders only to help identify good and bad traders.
It is up to the users to add the feedback once the deal is concluded, there is no moderator involvement. If you have a problem send a PM to the moderator of the buying or selling forum.
This is a great idea, whoever decided to implement it. Like other people, I'd also like to know if it's kosher to rate people that you've conducted past trades with, or if it's pretty much a blank slate from the upgrade.