An unhappy customer with a phone in their hand is a fork in the road. One direction is a private message you can fix. The other is a public rating you cannot.
Every review flow eventually meets someone who had a bad visit. What happens in the next ten seconds decides whether you get information or a permanent one-star.
When a customer taps two stars, sending them to a public form is a choice to publish the worst version of that moment. Sending them to a private note asks a better question: what went wrong, and can we make it right?
Nothing here blocks a public review, and it should not. Anyone can post whatever they like on Google whenever they like. What you can do is offer a faster route to an actual fix, which is usually what the customer wanted.
Most angry reviews are the only channel the customer could find.
Private feedback tells you things your public rating never will: the chair that wobbles, the Tuesday wait, the staff member who is short with people. That is free operational data, and it arrives before it costs you anything.