The only undercover stings are for guys looking for minors, and they'll make that clear. They don't have the time or money to waste on consenting adults, even if it's illegal.
The main thing you have to worry about with LeoList are girls with fake pics or who lie about their services, but that's not dangerous, just a rip off. I've heard stories about robberies, running into pimps, etc., but I think that's rare. The best way to avoid problems is to only see well-reviewed girls.
Verified is in relation to the pictures. If the girl holds up a picture with LeoList written on it, the picture is are verified, i.e. not stolen from the internet.