What's wrong with making music to get money out of it? People all get jobs to make some money. Are we all selling our souls then?
To me there is a difference between playing what the audience wants to hear in order to 'sell' seats and retain popularity and completely changing your style or staying stuck in one style because that is what is making you the most money.
Music is an art form and art thrives when the expression is pure and freely flowing from the artist. Some folks seem pretty good at faking it but it rarely if ever sounds as good as people who are literally playing from the heart.
To me 'selling your soul' is a metaphor for abandoning your principles or whole sound to appease a market. To me it is a crying shame how often this strategy pays off for those who do it but I don't think I've ever heard any improvement in a band that listened to what the marketing stooges told them to do.
There must be one r two out there but I can't think of any.
As for actually selling your soul to The Devil? I don't think that is possible and I believe. But then there is that story about Robert Johnson...
Funny thing about that. I knew a guy in school that wanted to play very badly before one summer break. When we all got back to school he was really good at hot dog licks in just the two plus months since he was a raw amateur. I always thought that was the most remarkable improvement I had ever seen in a musician.