(Disclaimer: I don't use craigslist, I've been to the site <10 times in my life, so I'm making assumptions about what's available to the end user in terms of reporting issues. If I'm wrong, I apologize in advance.)
In my opinion:
1 is unfair. You can't say with 100% certainty that any popular website is immune from something like that, so he can't say "yes". He certainly can't say "no" without making the site look bad. So how does he answer?
2 is unfair. If you ask about a specific ad, they can look in the system and say "that ad was placed on X, it was reported as problematic by a user on Y, we checked it on Z and reported it to the police." If you say in general "what are you doing about 'these girls'" then you're making him look bad by saying "I don't know 'which girls' you're referring to." Again, if you don't give him a chance to make a proper answer, then you're not really being fair as a reporter.
3 is similarly unfair unless he's at his computer and can give you the information. Obviously the post in question is crossing the line, but what do you expect him to do about it right then? If they manually screen the ads, then someone's not doing their job right, but can you say with 100% certainty that everyone at CNN is doing their job right 100% of the time?
Finally, 4 is unfair because if she'd actually reported the thing using the proper channels, then the post would have been gone before she'd have time to put together her story. But that would go against her interests, so it's much better to ambush him in person with an ad he's never seen before.
On the other hand, if the question is the less-personal and less-exasperated "why do you rely on your users to police your site?" then that's a fair question.
The underlying question for this reporter is this: Is your goal to get answers? Or is your goal to embarrass him for ratings?
(EDIT: replacing "stupid" with "unfair".)