I've always understood amateur to be someone who isn't paid to do something. So, that would pretty much mean NO content provider is actually selling amateur content.
Is it only girls that have never been seen before? You can get away with calling them amateurs until they get more than 1 gig and become internet saturated.
Perhaps it's the bad lighting look that defines amateurs?
As far as I can tell, the only REAL amateurs out there would be found at a place like
http://www.worldsexamateurs.com/