With Solution Settings you can allow the Contacts (who have permissions to view Solutions module) to Rate and Comment on the Solutions. You can even set the sort option for viewing Comments.
To configure Solution Settings,
Click on the Admin tab in the header pane to open the configuration wizard page.
Click Solution Settings icon under Helpdesk Settings block. The Solution Settings page opens.
Rating & Comments
Enable Solution Rating
Enable this check box to allow the contacts to rate the solutions. On enabling this setting, the option to rate the solution will be available in the Contact login.
Enable Solution Comments
Enable this check box to allow the contacts to comment on the solutions. On enabling this setting, the option to enter comments for the solution will be available in the Contact login.
Comments Sort Option
You can set the sort option to view the Comments on the Solutions page.
To view the comments in the descending order with the recently added comment at the top of the page, choose Newest first option or select Oldest first option to view the earlier added comments at the top of the page.