One Review per product
Is it possible to make it so, once they reviewed the product, their second reply would be without the ratings?
So your first post would allow you to rate the product. When you reply later one, it allows you to, but doesn't allow you to rate the product. Maybe remove the "rating" fields, and just make it a reply..
This something that is hard, or you would be interested? This may give what you mentioned the beta testers wanted.
The biggest problem with multiple ratings, you can get one member who rates the site 50 times. But the only way to stop this, is by allowing only one review. Doing this removes the ability to reply, to "chat" with others.