About selling your soul.
The entire notion has become fairly skewed over the years.
Let me give you an example. I know a demon, who was once a human black magician. As a young boy, he was indoctrinated into the Christian religion, but poverty and pain crept up and conquered him. Bullied by his peers, incapable of getting help for his diseases, incapable of getting anything he wanted. As a frail, weak, young boy he found himself literally crying in bathrooms. He was at a point of literally begging something to take his soul away.
And something did answer.
He did have some past lives which enabled him to connect more easily to the spirit world, but in essence, what he called ''the Dark Master'' answered. This ''dark master'' was his way of contacting the most dark thing he could conceive.
So what happened afterwards?
Well, besides having developed a mastery of dark magic, and other more general skills, he had money, power, good health, vitality, everything he could ask for really, and died peacefully, in his bed, of old age.
After his death, he was a spirit of the dead, and had to work towards becoming a demon, and after he did manage to do this, he is at a point where he has finally ascended past humans limits and accomplished his goals. Yes, he did ''become'' a demon, but this was/is FAR from a bad thing, since he is fairly powerful, happy, free, in essence, he had accomplished his goals.
How is that bad?
And even he can reincarnate, the only thing that selling his soul meant is that once he does/did reincarnate, he would always find his way back to the Dark Master, back to dark magic.
And ''the Dark Master'' is because he is the Master of Darkness, and not because he is his master.
That said, there are genuinely entities who do do the traditional ''I give you stuff, and in return you become my slave in the afterlife'' type of deal.
Then there are those who see the soul as Z'etoile, destiny. Selling your soul meaning giving up control of your destiny.
Common notions of selling your soul are flawed, I agree.
And who is Samiel? Any amount of research I found was for the angel Samael, who while demonic is by no means a demon, and is an angel of destruction and chaos, sure. The Venom of God if you will.
As for ''God'' well that's a different matter altogether.