If you post two "Casual Encounters" craigslist ads in the same city--months apart, at different times of day on different days of the week--you will get responses from the same guys.
The best scenario here is that they've got autoresponders that just spam every w4m with their dick pictures. The worst scenario is that they're really always there, always watching, always trying.
Is it hypocritical that I think posting to Casual Encounters every couple months is totally normal and healthy, but lurking there is super creepy? I don't think it is.