@Ross at Play
I would not refer to a salesman as a professional.
A lot of people don't.
They'd also be wrong, just as you are.
What happens with sales is quite simple. It LOOKS easy, so easy that anyone can try it. That happens quite frequently in our industry. And then when those people try it and fail, which most do, they denigrate those in the business because they feel that they should have been able to do it.
Being a professional salesman is not easy. You have to know relationships, you have to know your product, and you have to continually practice your skills to keep up with an ever changing client base as well as the new technology where your customers can reach you.
Note that Hollywood and even the industry itself have painted salesmen as slick hustlers. Those people do exist, those are the ones out for the quick buck. They're the ones who brag a lot, then end up can't make a living when times get tough. You are sort of correct in considering it the opposite of amateur, which is what most people who sell truly are - because they're not serious about their job.
Note that I am differentiating a salesman from a clerk. The lady who works at the fitting room at Wal-Mart is a clerk. (Al Bundy was a clerk.) The lady who helps you with a bespoke dress is (or should be) a salesman. It doesn't matter what industry you're in - you could sell houses, cars, medical equipment, copiers, or oil field equipment and services.
Most people in my field don't enter it by choice. No one graduates from high school or college and says, Now, I want to be a salesman. For me, this was supposed to be my fill in job when I moved to Oklahoma, until something better came along.
I've been doing it now for almost six years. I work with a guy who has been in the field for almost twenty. He basically works his own schedule, he has two or three repeat customers call him every day, and last year he made just over $400,000. I made just shy of $100,000, probably would have hit it if I hadn't had my heart issue. I'm still building my customer base, and I'm not from here, so I don't quite have the local base. We still read and attend seminars on how to improve our skills, we watch training videos, we make sure we stay certified on our products from the manufacturer, so we CAN sell them.
A clerk is not a professional salesman - and most people in our field are clerks.
In keeping with your professional versus amateur - and now to get into whether you consider something a sport or not, (Is it on ESPN? Then it's a sport.) I'm also a semi-professional poker player. By that I mean I practice - a lot - and I play - a lot - and I win a decent amount of money, but typically less than $50,000 per year. The professionals are the guys and gals who do this for a living, practice their skills, and typically have lifetime earnings in the 7 or 8 figure range.