How do I display different "No results behavior" based on exposed filter results and total results?
You could easily adapt the views-view.tpl.php to your specific view, eg, views-view--VIEWNAME.tpl.php and change up the portion dealing with no results...

&lt;?php if ($rows): ?&gt;
  &lt;div class="view-content"&gt;
    &lt;?php print $rows; ?&gt;
  &lt;/div&gt;
&lt;?php elseif ($empty): ?&gt;
  &lt;div class="view-empty"&gt;
    &lt;?php print $empty; ?&gt;
  &lt;/div&gt;
&lt;?php endif; ?&gt;


...with something along the lines of...

&lt;?php if ($rows): ?&gt;
  &lt;div class="view-content"&gt;
    &lt;?php print $rows; ?&gt;
  &lt;/div&gt;
&lt;?php elseif ($empty): ?&gt;
  &lt;div class="view-empty"&gt;
    &lt;?php if (count($_GET)&gt;1): ?&gt;
      Sorry, there are no results matching your search criteria.  Perhaps with other filters you may find some.
    &lt;?php else: ?&gt;
      There are no postings at this time. Please check back later.
    &lt;?php endif; ?&gt;
  &lt;/div&gt;
&lt;?php endif; ?&gt;


...with just some really simple logic based upon parameters Views uses for the exposed filters (eg, if more than ?q=PATH is sent it will have more than just 1 in $_GET).

Now if you want to get fancier than this you may want to investigate one of the Views preprocess hooks and actually change up the $empty variable and not put a lot of logic in the template.

If that's the case you could go further and re-run the View via views_get_view_result() without any filters and if it had any results, actually return your desired Sorry, there are no results matching your search criteria.  (You could do this in this template file but I really try to keep lots of deep logic outside of them)

(Is there any way to dynamically add a CSS class selector to a view with submitted exposed filters? has some more code you might be able to re-use here as well)