I thought of the same thing, or even something simpler, like zap-to-rate, so that you have to pay the author, in order to post a rating. Then only someone highly-motivated would bother. Freemium would have the advantage that malicious raters could get their contract cut and their ratings removed, so that would pressure them to be behave and stay constructive.

But I don't know. I understand that some users like giving the ratings, but others find the pressure to rate really irritating and refuse to do so (which reduces the signal of each rating, as it's a self-selected subgroup giving the ratings), and I question whether other users benefit from the ratings on-net. They seem to mostly be a way to press the advantage of big players (number of ratings leads to higher average ratings, in addition to their natural advantage of simply having lots of reviews and customers/users/bookmarkers), and reduce the visibility of newcomers, as everyone sorts the results by stars.

I'm not saying that I'm 💯 against it, but I'd be very cautious in implementing it and I'd be aware that the implementation burns all data bridges. You put it in there, you have to leave it in there forever. No take-backs.