I'd drop the term 'professional', and instead concentrate on commercial.

Professional can indicate that it is of someone's profession - meaning how they make their living, or it can simply mean that someone is an expert on the topic. You can be an expert, but not make your living on something, as it may be a hobby for you, or a former profession.

Example: I decide to close my business tomorrow, but I keep some pins around. After a period of time, I decide to sell one of my machines because my wife wants a nice lamp or vase in the gameroom, and the only way to make room is to get rid of the game I no longer play. The work on the game may be 'professional', the work I do on it to get it ready for sale is 'professional', but I am not a commercial seller. I'm just a guy selling a pin who knows a lot about the subject.

And the opposite way to look into it. Let's say my business slows, and I only sell 1 game a year. I'm still commercial, as I am still running a business. I'm just not doing much with the business!

A commercial seller is someone who runs a business. Someone who collects and pays taxes.

There are commercial sellers of any good with zero skills, and there are commercial sellers of that good with amazing skills.
There are hobbyist sellers of any good with zero skills, and there are hobbyist sellers of that good with amazing skills.

I would say people should self-police themselves. If there is a need for a commercial vs private designation on this site, the people running a commercial entity should put their stuff in their section.