How to know if it's actually a 404 page?
<p>What I learned from <a href="http://faq.foregenix.com/index.php?action=artikel&amp;cat=16&amp;id=15&amp;artlang=en">Foregenix</a>:</p>

<blockquote>
  <p>The HTTP 404 Not Found Error means that the webpage you were trying to reach could not be found on the server. It is a Client-side Error which means that either the page has been removed or moved and the URL was not changed accordingly, or that you typed in the URL incorrectly</p>
</blockquote>

<p>But then I also do web app pentests with Python and I am wondering that if I only check for the String <code>404</code> on the page, it may not really be a <code>404</code> error.
It can so happen that the page exists but the heading is <code>404</code> just to fool us.</p>

<p>So how exactly do I find out?</p>