yeah, I am dealing with the same thing. You have no recourse and helpless to anyone who would want to sabatage your reputation.
The good news is it's better to not have every review be five stars. That tends to look weird.
No matter how much technology changes things, the customer is still always right. I make sure that I let the reviewer (and everyone reading) that I acknowledge what they've said, and expess enthusiasm in making amends.
Graciousness goes a long way.