Professionals given no credit on forums..

[John Lifer]

Being an expert is not the same thing as being a professional. As others have pointed out, "professional" has different meanings as well. It may mean I do it for a living (I am a professional shoe shiner) or it may mean you are a member of a licensed profession (I am a licensed medical doctor, even if I choose to do research instead of treating illness).

An expert is someone who by way of education, training, or experience has more information about the given topic than their audience.

You can acquire expertise in multiple ways. I college I took astronomy classes, I have used basic techniques to precisely determine direction from celestial observations, I have read a biography of Columbus that described the navigation techniques he used, and this weekend I attended a presentation where some medieval devices were discussed and demonstrated. So I know a lot more about medieval methods of celestial navigation than the average person.

I might be an expert from the point of view of a boy scout group, but that does not mean I could usefully address astronomers at a conference.

Even if I could usefully address the astronomers, it would not make me an expert on infectious disease. The term is both topic and forum dependent.

I'll disagree somewhat with your definition of expert. In my opinion, you have to have a DEMONSTRATED expertise, not just be able to have more information. At least in most fields, you should be able to explain and demonstrate you know and have the ability to perform that expertise, and it isn't just being able to talk about it.
But yes, anyone can call themselves a professional or an expert and we can determine if that is accurate or not by their performance.
And I've seen plenty of professionals in many fields who are not experts.

[Mel Fulks]

I can accept something like “ I’ve been in this business a long time and have a good reputation, and would be glad to give you names of
people who like my work “. Much better than “ I’m the great Wizard of Oz , pay no attention to that man behind the curtain”.

[Mark Hennebury]

The problem as I see it, in terms of woodworking is there is only one yardstick and that is popularity. Advertising, promotion, bluff and bluster gets you well known, and popularity equals expertise, in the minds of those who do not possess the ability to judge for themselves.
In Karate for instance they are awarded different ranks after being judged by their peers.
In sword fighting, Miyamoto Mushashi stands tall as an expert, having the rare accomplishment of dying of old age.

[Doug Garson]

But yes, anyone can call themselves a professional

Try calling yourself a professional engineer or doctor and you may find yourself in court.

[mike stenson]

Try calling yourself a professional engineer or doctor and you may find yourself in court.

"woodworker" doesn't have a professional definition.

Also, claiming a profession you're not, on a forum, probably isn't going to get you into any legal issue.. unless, you start providing advice...