How to get posts using category slug in ClassiPress?

Well, I should have used the tax_query parameter. Something like the following:

$the_query = new WP_Query( array('post_type'=>'ad_listing',
'tax_query' => array(
    array(
        'taxonomy' => 'ad_cat',
        'field' => 'slug',
        'terms' => '7star'
    )
)
) );