Maybe I'm naive, but I think that it makes sense to look at online reviews before choosing venues for dining, working out, playing a sport, celebrating a milestone, etc. It's even more important to read online reviews for health care providers, other professionals and service people.
The key is to look at the overall pattern of the reviews as reviewing a professional, service provider, or venue is a highly subjective activity: people's expectations and tastes vary. As nobody and nothing is perfect, one reviewer can have a negative experience with a service provider, whereas five other reviewers can have a very positive experience with that same service provider.
As an occasional reviewer, I am more likely to only review venues, professionals, and service providers when my experience has been very positive unless someone has misrepresented his capabilities, behaved unprofessionally, charged me much more than the agreed-upon price without explaining why and getting my approval for the additional charges or work first, done what I consider to be a terrible job, stood me up, harmed me in some way, and/or was very rude. I would rather not post a negative review.
Some people take online reviews very seriously and I don't think that it's my place to ruin someone's reputation if he's not my cup of tea, if it appeared to me that he was having a bad day, or if my expectations were too high. Moreover, I don't have the time to review every purchase I make, every restaurant I try, every service provider I use, and my various health care providers.
In the same way that one should hold off sending an angry e-mail, I think that it's more just and more kind to hold off writing a bad online review. I'm not saying that you should never write a bad review: I'm saying that you should consider the situation for a day or two before doing so.
There is so much competition, these days, in every profession and business that your one negative review can make a difference in the livelihood of the professional or service provider.
Isn't it possible that there was a miscommunication or other lack of understanding that caused your dissatisfaction? What kind of mood were you in when you had your appointment with the professional or service provider?
In other words, there are three versions of a story: yours, his, and the truth and one should consider the damage that can be done before posting a negative online review.