I understand that sometimes people see reviews they dislike. However, that really is not an.excuse to delete reviews that have thoroughly outlined the negatives and positives for a work. I say this as I have noticed a severe issue with rating inflation. Ratings for novels are being falsely inflated by deleting low rated reviews and spamming high reviews either by xp or just the "shameless author" disease.
My suggestion is simply to not allow review deletions by the author. The author should be able to request their reviews to be reviewed to if they have a lroblem with one. Thus allowing more impartial judgement. Legitimate reviews should be left. Even if it is negative. Garbage reviews should be removed. Even if it is positive.
The inflation is bad and the pay walls are causing payment for stories that simply are not good. And after having paid for something you dislike you feel forced to continue to do so as otherwise you have to pay from the beginning for another novel.
TLDR; Rating inflation is a real problem. Deleting negative reviews only makes it worse.