Though the following comments are from an article on professional aviators, they are applicable to professionalism in every walk of life – including choral conductors.
Professionalism is a way of thinking about your work. Professionals don’t just understand the tasks they’re being paid to complete, they understand how all the pieces of everything in their profession fit together … and why. A professional (at least to me) understands the subtleties that produce a near perfect product or experience, whether that’s installing new carpeting in a home — clean up after yourselves and make sure everything fits before you leave — or flying an airplane near Virga — slow the airplane before you get too close since significant turbulence is highly probable.
And professionals wear their label proudly because they don’t need someone to tell