Disallowing a user for have little to no knowledge of hosting is scary to me.
Rather than Disallow new hosts, create a graded WhiteList of more established hosts. Not Rep, that's all about post tone, but something like Milestones. I've been doing Longevity. Other ones are somehow proving you are not a Reseller.
So then the "1-star" hosts can do their thing, but it will be clearer.