I believe that many of these people are against Saddam, but how do you tell who's sincere about it when there's still citizens fighting our troops?

The Iraqi people have been taught to dissemble for the past... what, twenty years now, simply as a basic survival mechanism. That's not going to go away overnight. It's not difficult to believe that they really want Saddam out, and are happy to see him go, but can you trust their outward expression of "yay America" anymore than you can trust their outward expressions of "yay Saddam"?