Had this exact situation โ client refused to pay final invoice, then left a 1-star Google review saying we "scammed" them. My instinct was to respond aggressively but my attorney talked me down.
What actually worked: A calm, professional public response acknowledging the disagreement without getting into specifics (avoid confirming they were even a client if possible โ HIPAA/privacy considerations depending on your industry). Then I focused on getting more positive reviews from happy clients to push the negative one down. Within a month it was buried.
If the review contains provably false factual statements (not just opinions), you may have a defamation claim, but the cost of litigation usually isn't worth it for a single review.