A small problem has been brought to my attention. I’m using the Description field to store the price, but the NewsListing snippet does not get the description field from the database or set it as a placeholder. I had hacked it to add that feature, and forgot about it! So it needs to be added to three places, in the $fields list in the main query, and in the $fields and $values arrays where the placeholders are set.
$resource = $modx->$callby($resourceparent, $sortby, $sortdir, $fields='id, pagetitle, longtitle, description, introtext, content, createdon, createdby, hidemenu');
...
$fields = array('[+title+]','[+longtitle+]','[+description+]','[+summary+]','[+link+]','[+author+]','[+date+]','[+id+]');
$values = array($resource[$x]['pagetitle'],$resource[$x]['longtitle'],$resource[$x]['description'],$summary,$link,$username,strftime($date, $resource[$x]['createdon']),$resource[$x]['id']);
(sparselogic, if you read this, your inbox is full...)