Professionals are people on whom editors depend. We don't just make our deadlines, we beat them. We're dependable. Many years I received opportunities to ghostwrite for a publisher—and did a total of 35 for them. Although I didn't know the reason for at least a decade, a woman had written many books for them and she was excellent. She had failed to meet every deadline. They got tired of working with her.
Another thing about professionals is that we take criticism well. We know we have things to learn. Even if we don’t agree with what an editor says, we seriously ponder it instead of responding with anger. A once-famous writer called an editor on the phone and berated her. The story I heard (from someone who sat there) was that the writer yelled and screamed for nearly five hours. Maybe that's a reason she's no longer a famous writer.
I could list other characteristics, but professionals seem to have an innate sense of the correct thing to do at the right time. Perhaps I could sum it up by saying that professionals try to be sensitive to others, especially in the way they treat people who are a few rungs lower on the ladder than they are.
I am a professional and I behave professionally.