Negative reviews are almost inevitable. We pride ourselves on being an honest, fair, and transparent place for peer-to-peer contractor reviews. Because of this, we cannot remove or edit factual reviews.
It is illegal to remove legitimate consumer reviews under the Consumer Review Fairness Act to “protect people’s ability to share in any forum their honest opinions about a business’ products, services, or conduct” (You can read more about the law HERE)
Try to rectify the rectify the problem by contacting the customer directly through the contact information they provided to you at the time of service.
A lawsuit over a review is not recommended. You may create a much larger problem than the one you started with, incur legal fees, and be responsible for other parties as well.
You can find tips on how to handle and respond to negative reviews, here.