Can we get back on topic please. I don't appreciate taking a very serious topic, and making it into a joke about hamburgers!
I'm here worrying about going to hell, and all you guys can do is talk about hamburgers!!!
If you're saved I don't think you could sell your soul. But then again I'm reminded of the end times where people take the mark of the beast and be damned forever, so I guess you can.
Most of the world is under the power of the devil, and so their soul in a sense belongs to the devil. However since God calls out and saves people it is not permanent, and so if your soul really is sold I think you can go back to God.