The method has been tremendously successful for science, as we've discovered what makes up the Universe, in what proportion, and what the force laws are that govern physical scales ranging from the subatomic to the cosmological.
Did Sammie sell his soul? I've written about how I think Sammie might have sold his soul. The end-credits scene shows him with no scars. That means that it takes place before the events depicted in the movie. Does he attract Remmick because he has access to another dimension? Is the scene showcasing Black music in the middle of the film a sign that he can tap into the divine because of an encounter with an otherworldly being? The next film could show us the answer.