In my zeal to track every Chalet remaining in existence, I learned the hard way a couple of years ago that some Craigslist ads are deleted by the sellers or get flagged for removal within hours. Now, the moment I see one, I copy the text and photos to my computer, while immediately printing out a paper copy.
In one case, the seller was amazed to receive my long-distance call a day or so after she posted the ad, because her husband had ordered her to take it down about an hour after she put it online.