Even though this is a Different Games forum, you can't do sales Black Market Sales on this forum because no one can hardly tell if it's scamming. There is no rules for you to do Black Market Sales on this forum, but you do it at your own risk, people who scam you on Different Games won't be affected by RuneScape Discussion meaning the player won't be banned.
If you do decide to do a Black Market trade on this forum, please try and get a Middle Man, or anyone to Middle Man for you, so you don't get scammed.
Remember, trade at your own risk!