I read a blog about selling out (http://profile.ultimate-guitar.com/thenextkirk92/ blog/39063/), and the thing that stood out to me was that he was defending Metallica. I want to express what I define "selling-out" as.
I think that selling out is when a band or group makes an album or goes on tour for the sole purpose of making money, and not thinking about their fans at all. Because a band makes a "Greatest Hits" album, does NOT mean the band sold out, they make that for newer fans that want to cut through the crap or want a album that has a lot of great songs.
So I think that thenextkirk92 has it wrong, while I agree that Metallica seems like they have sold out, Alice Cooper has not sold out just because he was in commercials, that's like saying Les Paul sold out because he agreed to only play in public with Gibson guitars, which he didn't.