A business harmed by an online review has limited routes, because the platform is generally immune.
Platform immunity. Providers of interactive computer services are not treated as the publisher of information provided by another content provider, which bars most claims against platforms for user content. The immunity does not extend to content the platform itself develops, in whole or in part.
Claims against the author. Defamation, if the statement is a false statement of fact rather than opinion. Reviews expressing dissatisfaction are usually opinion; a review asserting a specific false fact may not be.
Identifying anonymous authors. A subpoena to the platform, subject in many states to a threshold showing — notice to the poster, a prima facie case, and sometimes a balancing of interests. Courts quash these regularly.
Contractual restrictions. Federal law voids contract terms prohibiting or penalising honest consumer reviews, with civil penalties for imposing them. Non-disparagement clauses in consumer contracts are unlawful.
Fake reviews. Purchasing positive reviews or posting fabricated negative reviews of competitors is deceptive and separately actionable, with specific rules prohibiting them.
Practical response. A measured public reply, a request for correction to the author, and a platform flag for terms violations achieve more than litigation in most cases.