We are sorry to hear you had a negative experience with a seller.  Our User Guidelines and Terms of Use policy state in relevant part:

"RollaNet is not a participant in transactions between the seller and the buyer. We do not guarantee the safety or accuracy of items listed for sale, or the character of the individuals involved."

You can leave feedback on the seller using the 'Vote Now' text link found on the left-side menu.  Look for the blue bar titled "Popularity" just below the seller's other listings.