Time to state the obvious. There are famous pro modelers who are masters of their trade -- Gerald Wingrove, Juha Airio, the staff at Amalgam, Marvin and Jorge at modelmotorcars.com, Misko, Fine Art Models, etc. etc. etc., and a few others who are members here (I won't name them for fear of leaving anyone out). They sell models for hundreds of dollars, up to 5 figures. They write books. They have well-developed websites. It doesn't matter what category of models they build, and many of them cover a spectrum.
As long as you've got a steady stream of customers who give you a living, you're a pro modeler, regardless of the level of quality. As an ad agency creative director, I had to review the portfolios of multiple "professional" designers and art directors, and I don't know how many of them could support themselves with such a low quality of work.
As stated time after time here, the people who call themselves "pro modelers" on eBay are usually blowing smoke up everyone's wazoo, primarily their own.