what would be a practical policy on soul wheeling and dealing?

say at one point a person's soul was sold or traded either knowingly or in some way unknowingly and at a later point in their life they sold or traded it to a different...devil, could you use a sold soul over and over...is there some sort of knowledge or limit, could one person sell another person's soul?

at the point of death, who would the soul default to?

The soul > supposedly is immortal. To sell immortality is more likely your question. As for practicality, or policy?

You would have to understand, that the currency of ones soul is measured through ones immortality.