There's a transaction forum where you can post the deal. Either click on the HobbyInsider logo at the top of the page to list out all the forums, or use the Forum Jump list box at the bottom of the page.
One trader should create the post, and the other should reply. Then when the cards are received, post on the same thread that the cards arrived, and then you can use the link to that thread in the Trader Rating feedback.
Thanks,
Chris