So then that should not be causing the problem of them not being sorted properly. The code you have is correct.
<?php
$mypost = array(
'post_type' => 'listing',
'posts_per_page' => 20,
'meta_key' => 'revenue_number',
'orderby' => 'meta_value_num',
'order' => 'DESC'
);
$loop = new WP_Query($mypost);
?>
What is after this? What does you loop look like?
