Comment only once per node I'm trying to get my users to post only once on each Product node... I'm kind of new to hooks and I'm not sure what else should I use for this.

What is the drupal way to do this?
You can use the Comment limit module.


  Limits how many comments a user may post on a node.
  Adjustable on a per node type basis.
  
  This module can be handy for instance when comments are used as "Reviews" and "Ratings" for products and a user may only review and rate a product once.