In literature, "deals with the devil" always turn about bad. Why is that?

Couldn’t a devil (in literature) make a deal beneficial to both sides? After all, in contract law, a deal (a contract) must have two sides – a benefit to one side and ‘due consideration’ (meaning money usually) to the other.

So why couldn’t a ‘deal with the devil’ be mutually beneficial?

It seems like the devil is being unduly blamed.