Hi!
If you don’t want to show posts from a category, then you can exclude them on the Advanced Options panel: http://wp-dreams.com/demo/wp-ajax-search-pro3/docs/#advanced_options_excluding_categories
If you however don’t want to show some of the selectors on the frontend, then you can exlude those categories on the Frontend the posts from category on the Frontend Search Settings -> Categories & Taxonomies options panel: http://wp-dreams.com/demo/wp-ajax-search-pro3/docs/#frontend_search_settings_showing_hiding_category_selectors