Yea as others have mentioned I would class a gambler as professional  when
it is their only or main source of income and that they are making a living and or profiting
from that.

Somebody casually gambling would not be classed as a professional gambler IMO.

Yea as others have mentioned I would class a gambler as professional  when
it is their only or main source of income and that they are making a living and or profiting
from that.