It might be a good idea for your client to get good reviews in video format. Have them contact their past customers who are happy and would be willing to review them on camera. Post these video testimonials on YouTube and embed them on the client website.
You can also have the company create an "Brand Name - About Us" video which gives insight into the company for prospects. Explain how they do business and why they are best choice over their competition. You can also ask questions in the video and encourage watchers to comment.
If these videos you create have more interaction and more popularity than the other negative video, and is relevant for the same search terms (Brand Name) then that negative video will probably drop off the first page of organic / universal results.
