Disable the Write review Button so buyers can only write a review when they get an email or make it so only logged in accounts who bought the product can write a review.
We already have a feature in our Debutify Reviews app to show the verified reviews from the customers who had made the purchse from store. Our app has a feature to import the product reviews from other platforms and CSV so we can't limitize this to only buyers who had made the purchase, however there's a possibility to moderate the reviews within app which can help you to achieve the reviews from the buyers only. I hope you can understand. Thank you!