disagree
Professional means you draw your income primarily from that activity,
With this definition Michael Jordan is not a professional basketball
player since he makes most of his money from shoes.
Tax law has phrases like "business-like manner", which surely
must be relevant in a definition of the term.
It's probably easier to come up with a list of things which
constitute professional behavior and amateur behavior.
Sometimes a professional may act "unprofessionally".
Sometimes an amateur might have professional expertise in some
part of the game.
Here's some unprofessional behavior:
- playing with a fellow counter at the same table, raising and
lowering your bets roughly in unison
- quitting a lucrative game because the guy on 3rd "doesn't know
how to play right"
- trying to impress a PB with how smart you are
- bragging at every cocktail party about how you play with an
advantage and have been kicked out of casinos
- quitting a trip early when you are up in order to feel good about
the win
Here's some professional behavior:
- encouraging people to think you are an idiot/loser
- when important for the best conditions playing by yourself rather
than with friends
- keeping scrupulous track of wins/losses, as well as observations
of conditions/staff
I'm sure people can add to these.