Craig's List for anything should make you cautious right from the start. My former boyfriend is a photographer and when he needs models to show a lot of skin, he lets them know they may bring a friend or guardian so they can feel safer. In fact, serious photographers know the model will look better more confident when they feel completely safe and have friends to support them. So tell the photographer you want to bring an assistant and see if he says "never mind".
Uh... no, but please don't do this. They're out to see you in less than underwear & more in sexually "compromising situations". Very dangerous, not to mention ruining your reputation & possibly your life. You have no idea who these people are or where these pics will surface.