"Who is the girl with no pictures that replied to me? She must be ugly"
Don't be so certain about that. I have met a lot of hot girls who just wanted to be discreet.
I realize now after many conversations with women whom I've met on CL why it is so much easier to work than the paid (and even free) personals. A lot of females do not want to post their picture online in this context. Most paid personal services require that you submit a clear photo of your face. Not only that, you also have to spend a good hour or so completing a profile form. For the person who is just "experimenting" this is just too much of an investment. Remember that women like to try new things and "see what happens." Going through the application and submission process for a personal service is a solid commitment that says "I am lonely and I can't find a man in the real world." Replying to ads on Craigslist without a picture is not only anonymous but also perfect for the whole "If it's meant to be..." mindset.
"So how do I find out what she looks like without wasting a lot of time?"
Well, if you subscribe to my newsletter you already know the answer to this one. If not I suggest you sign up today for the only newsletter written specifically for meeting attractive girls on CL. Just send an email to firstname.lastname@example.org