I am blues musician because I am a professional grade blues harmonica player who plays mostly blues music. I am not a "bluesman", however. That term is covered in so much mythology and wishful thinking that it has come to represent qualities and essences that are intangible, inestimable, and vaguely metaphysical. That is to say I think the term "bluesman" is a little pretentious when applied to most good, honest musicians who specialize in blues styles. I am a blues musician, verifiable in fact, not dependent on someone else's criteria. The definition of "professional" is slippery, and perhaps I shouldn't have mentioned it.
That is why I qualified my remark with the attending term "grade", meant only to say that I am good enough to be paid for playing the harmonica if I wanted to go that route. Alas, I do not have a recording contract, but the world is full of working harmonica players as good as or better than I who are similarly unattached to a record label. That fact does not diminish their professionalism, nor diminishes their skills as harp players. I would say a professional grade blues harmonica player is knows the changes, knows the key differentials, gets the tone and emphasis right, and is able to fall back, accompany, or lay out altogether when he or she is not taking a solo; this is to say the professional grade blues harmonica player listens to what the others in the band are doing and adds to a quality musical experience, not dominate it.
Mostly, though, the professional is paid, and the amateur is not, strictly speaking.