What determines the success rate when posting?

When you manually post to a blog, sometimes it will kick back and say something like "Your comment was successful".  When scrapebox receives this message it reports the post as successful.

If scrapebox does not receive a message to this extent, it reports the post as failed.  If you have done much manual blog commenting you know that that doesn't mean it failed.  Sometimes it simply accepts your comment and redirects you back to the post without any notification, or something else.  The comment might be successful in this case, but it just didn't kick back the notification so scrapebox can't report that it was successful, so it reports failed.