In theory, it is possible to sell your soul, as suggested by the Christian messiah in the bible. In the four gospel books, Jesus likens the soul to valuable treasure that cannot equal worldly fortune, and asks why one would even think about selling it.
The bible makes 32 references from both testaments about the soul. One reference states that a person can forfeit his soul in his quest to gain the whole world.
In the new testament, Jesus makes a reference to the soul, by wondering what one substitutes for his soul, and what one can possibly give to get his soul back. Furthermore, Jesus says that he paid for the souls of sinners with his blood, suggesting that he has indeed bought the souls of individuals who believe in him.