User can contact seller directly from product page. Option to set so that user can contact seller only after purchase.
Please use https://wordpress.org/plugins/front-end-pm-woocommerce-integration/
Once activated, user can send message to seller directly from product page.
You can go to Dashboard > Front End PM > Settings > Misc > WooCommerce to set if you want your users can contact seller only after purchase. You can also set in which order statuses customer can contact seller.
Screenshot:
This is a community maintained custom extension. There are lots of plugins for integration, so it is not possible to maintain all. I do not provide support for this extension.