We should return perhaps to the very English idea of what an amateur was in the 19th century. Most of these amateurs (who loved what they did) were wealthy enough and did not have to work. Many were mountain climbers, gardeners, botanists, artists and archaeologists. There is a remnant of this in the 21st century related to the starving artist that does not sell out.
As a retired professional photographer I always told people that if you sold a photograph for one cent that instantly made you a commercial and or professional photographer.
My idea of the professional is the person who is able to provide something related to his or her profession on demand and withou any excuses.