Hey @(you need an account to see links),
If you were selling something from the [GROUP] NC WTB/WTS thread, then you would need to locate the most recent post you made containing the items you had for sale You would be able to select "Selling" then. If you bought something from a listing made by another user in the [GROUP] NC WTB/WTS thread, then you would be the buyer and not the seller, so the "Selling" option would not be available in that case.