How about if a customer rated BAD stars (from 1 to 4) and we have no way to contact him or he is just a competitor?
I see Envato is still stuck in this problem many years and has no solution. But I have an idea which can help you solving this problem easily and help your market having a positive environment.
If a customer rated 4 stars with Main reason: Customer Support (actually, he did not send any support ticket to you), you can remove this review if your TWO future reviews for Customer Support are all 5 stars (those 5 stars reviews do not need to be consecutive).
So on, we need THREE future 5 stars reviews to remove a 3 stars review, FOUR future 5 stars reviews to remove a 2 stars review, and FIVE future 5 stars reviews to remove a 1 star review.
This rating system will encourage authors upgrading their item features and support services to whole new level to make BAD reviews become outdated.
Hope to hear both author and staff opinions about this system.