Legal and accounting work is chosen on credibility, and prospective clients read reviews as evidence of competence. A review alleging negligence, overcharging or a lost outcome carries real weight even when it comes from someone the firm never acted for.
The response options are unusually narrow. Confidentiality and professional obligations mean a firm generally cannot confirm whether a person was a client, correct the account of a matter, or explain the context — and a bare, careful reply can read as evasive to anyone who does not understand why.
That is why the policy route matters here. Google will not remove a review because a firm disputes it, but reviews from parties with no client relationship, from an opposing side in a matter, from a competitor or former employee, or containing private information or personal attacks can be assessed and reported without disclosing anything privileged.