There is a level of privacy that the on-line review site must maintain in order to give validity to the good reviews and a lot legally for you to have to prove to get them to release the information to you or remove the reviews. You are going to have to speak with an attorney and give him or her more than just supposition but concrete evidence that it is your competitor and then maybe you can even go after them.   Maybe.  But it may be best for you to deal with the review in a calm and professional manner, same as you would if that customer came in complaining. Maybe offer the customer a replacement or refund if they were not satisfied.  Depends on the product and review.  But ask your satisfied clients to write positive reviews and that will help tremendously.  Good luck.