A couple recent comments:
1) An amateur is a person who is not a professional, a professional is
someone who is paid for their skill(s). Nowhere does it say that
either is competent or incompetent. Many amateurs are vastly more
skilled than professionals operating in the same area.

2) I am an amateur radio operator in the classic definition, that of one
who loves the activity, not in the much more recent corruption of the
word - that of non-professional or shoddy.

Most very strange in a world where I can perform most activities
much better than th eso called professionals.
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pro - does it for money. Implies that there is some
(financial,reputation) responsibility for results

amateur - does it for no money (e.g. for the love of the activity, see
the Latin root of the word).

Proficiency, competency, or skill doesn't really enter into it.
Although, an unskilled professional had better be a good salesperson,
because otherwise, nobody is going to be willing to compensate them.

Lord Rayleigh was an amateur: nobody was paying him to do his work.

It's also true that a pro that has been in business (successfully) for a
number of years is likely to be competent. (or they'd starve).

An amateur can get away with being incompetent for years without ill effect.

In some fields (Engineering, in the United States), there are some legal
aspects to being "pro" aside from being compensated. To call oneself a
Professional Engineer, one must have a certain amount of experience (6
years, typically) at engineering, have passed a couple of fairly
rigorous tests, etc. so that you have a license. One could acquire the
experience while unpaid, and certainly one doesn't get paid for the
test, so one could be an amateur Professional Engineer.