Where do posts get the sidebar from?

get_sidebar() accepts a parameter $name. Then will look for a file sidebar-{$name}.php.

So what you can do is:

get_sidebar( get_post_type() ); // search for sidebar-post.php or sidebar-page.php

or:

if ( in_category( array( 'featured-listing', 'listing-post' ) ) )
    get_sidebar( 'listing' ); // sidebar-listing.php
else
   get_sidebar();