@Linkat,
Any time you are answering ads online (or otherwise) one should be cautious.
I know what you're saying about concerns with Craigslist; however, the problem is that when you're on their Personals ads page is that there've been ads for hookers, pimps services, etc. In fact, Craigslist has been taken to court over their policies for personals ads.
That being said, people who are looking to share their space and place ads are, for the most part, pretty legit.