Classified Ads 3 defines a Context 3 condition plugin.

This plugin is implemented in plugins/classified_context_condition_path, and allows you to define a condition on the non-node pages controlled by the Classified Ads module: its main page, its listing pages, its settings pages, and the "Ads" page for each user account.

To enable that condition when defining a context, choose a path condition, and check the Auto Classified path set checkbox. The module paths will be automatically added to the list of paths you define manually when you submit that form.

If you want to also trigger that context on Classified Ads node pages, add a Node type condition to your context, and check the Classified Ads checkbox on the node type list. Make sure you have not checked the Require all conditions checkbox.