Hi there,
I understand receiving reviews is an important aspect of keeping quality within your business, and spam comments can be an endlessly frustrating endeavor.
What I can do is recommend this guide: https://wholesalesuiteplugin.com/stop-spam-woocommerce-store/
It provides helpful tips on keeping your reviews spam free.
And just for your further consideration, should you want more control on how you handle reviews within your WooCommerce site, we have a plugin that can allow you added functionality on reviews, our WooCommerce Product Reviews Pro.
This extends the core WooCommerce product reviews functionality. It adds several new functions to product reviews, and can also enable different “contribution” types from customers, such as comments, questions, photos, and videos.
Hope this helps!