Drupal commerce based recommendations engine
I would not use comments to be recommendations but I would use nodes. This will give more flexibillity.

Here is a possible architecture:

I would use the flag module to let user flag (recommend) a product.
On flagging, I would use hook_flag to create a new node (content type: recommendation). This node would reference to the product. The new node would contain a body field that will contain the actual recommendation. Finally, I would attach the rate module to this node so that users will be able to vote on it.

As far as I know the flag 3.x module is now an entity, which means that you can attach fields to the flag. So, another possible architecture would be to use the flag itself for storing the recommendation. Have not tried this though but seems interesting.