So from what I understand is that there is a similar website or bad review showing up on the first page somewhere, and you are just trying to get rid of it. In hopes trying to buy more websites and rank them to push it out.
If this is correct, then first if this "negative" result is any type of slander towards your website contact google and they may be able to remove it. Also you can try to resolve the bad review with your own comments and voice some type of refund, to the unsatisfied. That would be ultimately cheaper.
If that's not the case, then yes you can buy a bunch of domains, but it all depends on your keywords and how hard it is to rank. You would have to spend the money and time SEOptimizing each individual domain. And review sites are not easy to rank over with a new site, it sounds like the this review site/page has a lot of authority and a brand new domain will not magically rank over just cause it has the same keywords. (at least not anymore) Same Name Domains don't hold as much authority in google as they used too.
Another route you can take is getting better reviews, you will always get bad reviews that's just how it is, try encouraging the people you have worked with that has had great experiences to share them on the review sites your trying to push out the way.
Just trying to think out the box, the bottom line is like every one said is that its going to cost a lot of money and more importantly time. But if you really want to go the SEO route I would still go with what Seoguevarra said, point off site seo efforts to all your social platforms.