Yes, seek local counsel!
I am licensed in Calif., not Maine, and anyway lawyers here cannot give specific legal advice here because no lawyer-client relation exists.
I presume the cause enumerated in the lawsuit is either libel or tortious interference with contract?
Libel online follows the same rules as libel in print.
If it was a legitimate review, even though negative, libel will be difficult to substantiate.
If the "review" was an unusually vitriolic rant and contained specific allegations of criminal conduct, such as illegally deceptive or fraudulent business practices, or violations of personal privacy (not on a matter of public importance), there may be a cause requiring legal defense.
So seek local counsel!
Tortious interference with contract is a cause where a third person intentionally interferes with the formation of a contract or with an existing contract, such as inducing one of the contracting parties to breach the contract, denying the other contracting party the benefit of the contracted bargain.
With respect to an online review, we're probably talking about allegations of thwarted future sales: this argument is usually not received well by courts, because "future sales" are almost always too speculative and difficult to prove. Also, the plaintiff in such an action would have to show that it was that one specific review that thwarted one or more specific sales, and no other reviews played a role. That's a pretty hard row to hoe!
Good Luck! And if you found this perspective helpful, I would greatly appreciate a positive rating! Thanks!