I'd never look for a plumber there, nor doctor, nor a brake specialist. Definitely not where I'd look for in regards to a photographer.
I understand what you are getting at but I don't think the analogy is a good one. The professions you mentioned are for professionals that need to have some kind of certification for safety reasons. Finding a photographer or other artist on Facebook isn't going to cause the potential harm as if person's house got flooded, or a person was wrongly diagnosed, and if a car bolts through a busy city cause the brakes don't work.
Facebook is one of the most powerful forms of marketing and promotion for artists. Most photographers probably have a business of some sort and rely a lot on word of mouth communication of past clients recommending you to their friends, co-workers and family. With Facebook, it's easier, more powerful, and instant. You don't even need to hope your clients somehow find it amongst themselves to bring up their portrait session in a conversation. All that needs to happen is an acquaintance of a past client easily sees a photograph somewhere on the Facebook page. And if you are on facebook all that acquaintance needs to do is send a quick message to your past client, or click a few times and be on your page with all your details where they will instantly access more images that might inspire them to book a session.


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