In Australia, and I imagine the rest of the world, there were many people calling themselves astrologers who barely knew Sun Sign astrology. When we set up the Federation of Australian Astrologers and its exam system the goal was to produce astrologers who were reasonably competent in our craft and could prove it through their exams. This isn't any different to most other professions. We did quite a bit of publicity to inform people that the study of astrology took a number of years and mentioned the schools which provided a good astrological education and qualifications so people would know that at least they were receiving a reasonable level of competence.
Astrological qualifications are a good option for anyone wanting to become professional but it doesn't end there. An astrologer must let go of all preconceptions, prejudices and judgement so she or he can be of proper service to the client - and believe me this can be very testing indeed because an astrologer regularly deals with great traumas in the life of clients. An astrologer can't try to make the client fit the chart but needs to observe how the client is using the energies provided by that birth moment. This is all gained through experience and the only way a person can get experience is by doing lots and lots of the charts of real life people with real life problems.
So part of the process of becoming professional is to get some qualification from a reputable astrologer or astrological school and then offer to do the charts of people for a reduced rate, explaining that you are a beginner and want to practice - and then actually discuss the chart with the client rather than pontificate. When I taught this is was part of the curriculum for the 4th year of study and interestingly, generated quite a few clients for the pupil; they started with friends and then the word went around.
The ability to be able to accurately forecast, choose good times for starting something (electional astrology) and answer questions accurately and clearly, is essential.
There are exceptions to the rule. For example, a colleague and I had the same teacher but she never received any qualifications (basically because she hates being told what to do), however she developed a good level of competence and has became quite well known. Currently she has her own very popular radio program. She has kept up her astrological education and, because of her years of experience, is certainly better than many of her juniors. I suppose she is semi-professional as she had a high profile profession in another field but continued to see clients, write articles and give talks in our field.
So overall I agree with mdinaz - it boils down to 'show me'; one chooses the astrologer who will be able to give you what you require. If you develop skill clients will come, but most people need a back-up job for hard times as running your own business, particularly astrology, is very hard with considerable fluctuations. If you are lucky enough to write a book or books that catch the imagination of the public or fellow astrologers you can make money through workshops, talks etc., and the client base increases as well, but this doesn't happen to most of us.
Alice