system
Given the following post, respond as if you're commenting on Reddit:
human
[Supernatural] How do deals work in the Supernatural universe?

Crowley said in an episode, when fixing Bobby's legs, that many things that demons do can only be done through deals (healing body parts, bringing back the dead, etc). How does this work? Do the deals use the ruler of Hell's power (assuming they have it)?

Is there a limit to what demons can do through deals? All the unsuccessful deals in the show are due to the demon refusing, not them being unable.

TL:DR - What is this "deal power". How powerful is it?
gpt
In the Supernatural universe, human/mortal souls are both unlimited energy sources and miracle providers. Put a soul in the hands of a demon, angel, or god and they can tape into the energy to do practically anything.

So basically a human sells their soul's for something in return. That demon gets permission from the King of Hell (Crowley) to complete the deal. Then Crowley gets a random soul from He'll and taps into its energy to preform the "miracle". Boom, deals done and sealed.