"Company-controlled review websites."
Well.. this one is unrealistic.
If you're selling products on your site, it's a reasonable expectation to provide customers with a review feature. For example, if I had a small business which sells a few of my products directly from my own site, I would have these options:
1 - Include a simple customer review feature for the benefit of the customers. This could be as simple as using an existing reviews/feedback plugin for whatever software I'm using to run the site.
2 - Pay some "independent" review service to handle reviews, potentially leaking personal customer information to that company and/or requiring the customers to sign up on some other random service (and agree to their arbitrary terms of service) just to leave a review.
3 - Not include reviews at all. And if I'm a nobody seller, I probably won't even be enough of a drop in the ocean for any free 3rd party review site to include my products. And certainly without any coupled options, such as "only show verified purchases".
So if #1 is outlawed, and #2 is a waste of my money for something that has no significant ROI incentive (other than being a "nice" thing to provide to customers). that only leaves #3, which just punishes the customers.
Now f you want to prohibit a company from using access to their own website from manipulate reviews, that's fine. This would be no different than prohibiting a search engine promoting their own products over competitors.