Although many things are traded in the Demonic Realm and bartering is not uncommon, the primary currency is Favors.

Favors are exactly what they seem, and can be traded with other Demons, they can be added to other Favors, and they can be slowly paid back or added to. Demons seem to have an incredible ability to remember "owed Favors" and decades can go by before they are cashed in. Demonic Masters accumulate Favors endlessly by their underlings in exchange for protection, food, training, etc.

A True Favor is bound with energy to have a deep connection to the Demons very essence. Possibly because they are so energy filled, binding vows are extremely powerful to a Demon. 

In this small way Humans are "less trustworthy" than Demons, in that they can easily break their vows with very little consequence.

-Notes on Demonic Society, by the High Priest