If you haven't, apply for access to the Equipment Exchange.
Then read the stickies on how to use it.
List your Gold Cup in the Exchange of Pistols and Revolvers Sub-forum.
Look at the listings there to give you an idea how to do it.
Take good pictures of your piece showing the good features and the bad.
Be totally candid and honest in disclosing everything you know about your gun, like number of rounds shot, blueing/finish condition, function problems if any, accuracy, accessories, method of payment.
There is a feedback system in place that allows buyers and sellers to rate each other, so all members can see how good you are as a buyer or seller.