@boots – When I read the question, I looked at it from the point of view that it would be sold to a not so friendly source. Without completely invoking a religious conversation, I’m thinking the Devil. It’s the first thing that came to mind.
However, now that you are asking why, it makes me look at this in a different direction. I guess, when I was at the height of my fight w/ cancer, I did offer my soul for the favor of health. “Please God, if you save me – if you make the cancer go away, I’ll do whatever you want me to do.” In a sense, that could be considered making the offer to sell one’s soul. (and no, I wasn’t “cured” right away.)
I just lean more to the automatic thought of someone selling their soul to the devil. what does that say about my thought process?