What if a second page, featuring only 'Approved' reviews, was made, without getting rid of the actual one?
Each page could have an maximum capacity on how much they could affect the ratings (2.5 to 2.5)
The Author can only 'Approve' reviews with more than (X) Likes, and were posted by an account over (X) Level.
The Maximum Capacity of the Approved Page would be decided by an Average of (Number of Reviews) and (Rating given by these reviews)
The Maximum capacity may freely decrease, buy may not increase over 2.5
If the author has abused the power to approve only reviews over (X) Stars, the Max Cap may decrease, can be accounted based on [Rating of reviews approved by author] and [Rating of Normal reviews]
When a review is approved by an author, it can be Upvote or downvote by readers, but this is limited to those above (X) Level, who spent above (X) Minutes reading novel.
If Approved review is downvote enough times by readers who posses these numbers, it may be marked with 'Unpopular' and remain so until upvote enough.
Readers (possessing the numbers stated above) still have a Maximum capacity of Votes they can give.
Reviews not approved by Author still can receive votes though, and be 'Approved' by the general public. This general public still have to conform to the conditions before voting.
I don't know what more to add and whether this would work or not. I'm tired after tipping this much.