WP_query is not returning the expected result

Try using this:

$args = array(
    'post_type' => YOUR_POST_TYPE,
    'meta_query' => array(
        array(
            'key'     => '_wpcf_belongs_marque-type_id',
            'value'   => $parent_id
        )
    )
);

In your loop set an else statement just to sure that you query isn’t returning zero results:

if ( $the_query->have_posts() ) :
    while ( $the_query->have_posts() ) : $the_query->the_post();
        $output .= '<li class="active-results">' . the_title() . '</li>';
    endwhile;
else:
    $output="No items here :(";
endif;

Hope it helps.