a contract in which a person or a family member was sold into servitude or slavery; used in modern times to describe an unfair labor contract

To abandon one's integrity and principles to seek favor with a powerful person; to join a powerful group or the enemy camp for personal gain.

Selling one's body into servitude to pay for a father's funeral; famously refers to the story of Dong Yong from the 'Twenty-four Filial Exemplars' who sold himself to bury his father and was later helped by a celestial maiden.