Surely warriors are all amateurs, professionals are soldiers.
Sorry for coming to this a bit late, but, given that I have OED Online access and am not afraid to use it, I checked what the OED says.
Warrior: ‘A person whose occupation is warfare; a fighting man, whether soldier, sailor, or (latterly) airman; (in eulogistic sense) a valiant or an experienced man of war. Now chiefly poet. and rhetorical, esp. as applied to the fighting men of the ages celebrated in epic and romance and of pre-industrial peoples, for whom the designation soldier would be inappropriate.’
Soldier: ‘One who serves in an army for pay; one who takes part in military service or warfare; spec. one of the ordinary rank and file; a private.’
I’m not sure if that clarifies or muddies the waters further, but it would appear that all soldiers are warriors, while not all warriors are soldiers. Viking huskarls whose job is to make war, and who get paid for this purpose, are, by this definition, soldiers and warriors, while the local levies whose duty it is to turn out and fight may be soldiers without being warriors.