WordPress Plugins: Approve Buyers Comments WordPress Plugin
The plugin helps you to automatically approve comments from people who purchased one or more of your products (buyers) and puts the rest (non buyers) into moderation.
This can help you to interact with your buyers in many ways :
Collect testimonials and reviews from buyers.
If you’re releasing product updates, you can get feedback and questions from your buyers only.
You could also setup a quick post for support (faq’s) where your buyers could interact with you.
Everything without having to deal with spammers.