In theory, yes, they should and that's why it's a thing, but unfortunately the majority of people blow their experiences out of proportion and type with their feelings and not by the facts. This is a industry where the term "beauty is in the eye of the beholder" exists, because one person may really like my style, and another may look at it and call it "wrong", because I left the head a little too fluffy, or not fluffy enough, or I had to shave their dog because it was so matted their skin is raw. So someone will review just because they don't like my style or because we had to do something they didn't want to do, so they're unhappy and need some sort of justice for it to make them feel heard, and it goes: "They did my dog's haircut wrong/they shaved my dog and I told them I didn't want that, crappy groomers, don't go here.". That's my name smeared, when I did nothing wrong.
Now, people who are happy typically don't go out of their way to review a shop unless they're feeling overwhelmingly satisfied with a service, but how often does that happen? Do you go to your local drug store and review them afterwards because the cashier was nice to you? Not very many do.
Online reviews cause more problems than help us.