if you may, let me share with you, what the term 'professional photographer' means to me.
it doesn't just mean someone who makes a living by accepting pay for taking pictures.
first of all, he/she is someone who has a very good understanding of light and lighting, and how to manipulate it to affect photography. no matter presented with whatever kind of situation, location or subject, the professional photographer would be able to deal with it. he/she would not be stuck with, let's just call it a shot-block, where the photographer spend a long time, if not hours, wondering how to shoot it.. either due to lack of preparation or knowledge. whether it's getting right angle, selecting the right lens, lighting it the way its meant to be etc, he/she shouldn't fear or be daunted by the task.
challenged, maybe, but not handicapped by it. if the shot is impossible to pull off, he/she would be able to professionally handle and provide an alternative solution.
secondly, a professional photographer should be able to conduct him/herself in a professional manner. in all sense of the word.
also, this may sound a bit coarse ... if a photographer who calls him/herself 'professional' .. and markets him/herslf to a certain niche, eg. fashion, it better be because they are really good at it, has a very good future and strong interest in the subject matter etc. and not because they do not know how to shoot any other things.
lately, there have been an increasing number of individuals who have made their first step into 'professional' photography by shooting PR events and weddings... an area traditionally volatile in terms of market rates. while there is no particular need to regulate the 'market'...as this should vary according to the skill/experience level of the photographer and expectations of the client... we should all hope the photographers charge appropriately according to their professional standards, and not because of 'stealing' market.