A business owner is posting fake negative reviews against the competition on yahoo reviews?

The owner has own posting for yahoo reviews and creates fake yahoo IDs to post 5 star reviews for owner's business....then uses these fake IDs to give the competition negative and false reviews. Also reports any negative reviews for owners site to Yahoo, who then removes them. One of the negative reviews owner had removed was information regarding a legal infraction (owner is licensed and violated terms of the state board and was prosecuted for such). Anything to do to stop these negative reviews of the competition, and false positive reviews/postings of the owner's site?