what do you mean by "some well established consultation companies use freelancers platforms to market their services and get paid" ? how they use freelancer platforms?
Sorry for that. I've hired couple of consultation companies on freelancers or elance (can't remember which for sure), it think it was working quite well for them.
http://techcrunch.com/2014/08/20/service-marketplace-thumbta...
http://www.thumbtack.com/