How can I use the Comment field as a way to privately message the node author? I am working on a classifieds site where individual users can sign up and, of course, post things they would like to sell.

However, I need for users, both anonymous and signed up, to be able to contact the poster about his or her item.

Using the default comment form for this would be perfect.  What would I need to do in order to allow only the author of that node to see the comments for his node? I don't mind writing a module if I need to, but I am not sure how to get started. Even if I had to go that route, sounds like I would need to modify the permissions setting?

I know there are other modules out there like Private Message, but that's just too big and bulky when Comments work almost exactly like I need them to.

Thanks!
I see some potential pitfalls with this approach:


It probably won't be quite as simple as you describe because I guess you'd also like commenters to be able to see their comments, and replies to their comments, while hiding other people's comments. (Or am I wrong?)
You mention you'd like to allow anon users to comment, so you need some way to differentiate one anon user from another (if they're able to see their own comments, but not others).
It won't play nicely with page caching (at least without a bit of effort).
It might make life a bit more difficult if you want to have normal comments on a content type at some point. (Eg. should the comment moderation tools be showing comments which are actually private messages?)


If you do want to go down this route however you can use hook_node_view_alter().