Whether you are the buyer or seller, you can leave feedback one of two ways.

1) Go into the ad. In the Buyers/Sellers Tools, you will see a Leave Feedback link.
2) If you are the seller, go to the My Ads page in the My Market area of the marketplace. If you are the buyer, go the My Offers page in the My Ads page of the marketplace. To the right of your ad or offer, you will see a Rate link.

Please note that in order to be able to post feedback, the buyer must have made an offer through the ad using the Make Offer tool and the seller must have accepted the offer using the tools provided to the seller in the ad administration tools either through the ad or from the My Ads page.