Sam said:I don't know a single thing about professional poker players. So if you don't mind, I have a few questions.
1) What makes a person a professional poker player?
Well, different people have different definitions on this subject, I don't think there is a common definition. The one that I accept and use is that poker is the professionals primary source of income. Other definitions that others accept is a reliance on the income from poker for living expenses, while others say playing 20+ hours a week (although this is a very poor definition)
2) What happens when 2 or more professionals meet for a game, who loses? Would the loser still be professional?
I think that you are using the word professional here in the wrong sense. If there are 2 or more professionals or good players at a full table then everyone's expectation/winrate goes down or poor players lossrate increases further to the negative. A player that has a very modest winrate will increase to a losing winrate if enough good players join the game. It's mainly just a skill level thing. You could have a table of 10 amazing players, none of which are professionals or all of which are professionals, and have no one have a postive winrate because of the rake. If two players with the same skill level (although this would be incredibly rare) play against eachother then in the short term the luckiest one will win and in the long run and the casino wins as they have the same expectation and just grind eachother down passing money back and forth as the casino slowly takes it
3) Is it customary for a professional to introduce himself before playing with strangers? "Hi, I'm Jack, and I'm a professional poker player. May I play?"
Haha, well, it's not customary. As a professional myself, I would prefer that no one knows that I am paying my rent with their money. Typically only professionals can tell if other players are professionals based on plays that the professional makes. Nearly all recreational gamblers don't pay enough attention to the plays that other players make in order to tell a mediocre player from a professional from a good player. I've been called the worst player in the world many times before.
The difference between a good player and a professional is that a professional must be a good player while a good player is not necessarily a professional.
EDIT- Also, when discussing winrate or lossrates, it is important to understand that winrates don't converge until many many hands have been played. For example my winrate is about 2 Big Bets Per 100 Hands in your average midstakes game with a standard deviation of about 17 Big Bets Per 100 Hands. As you can imagine it can take over 100,000 hands in order to get an accurate representation of your winrate.
Hope that helps.
John
EDIT- Also edited for clarity.