Nothing personal but you completely missed the point of this thread.
Just a quick update. All our craigslist ads that had images with links to our church pages have scrolled off craigslist for a few weeks now, and we are now top hit for some incredible but relevant searches again, with no other real changes to our pages. I am pretty positive that there definitely is a craigslist penalty, and I think it has to do with images in multiple concurrent ads that link to a website when clicked.
I still think that you are seeing something totally anecdotal and coincidental.. If it were really that easy to push sites around in the SERPs by just running CL ads everyone would be doing it to hammer their competitors..
I have some craiglist ads up for a rental site I own. No SEO is done on the site as it's really just a brochure site. I checked its position today for its most targeted phrase and I am now deleting the craigslist ads and will check in a few days and see if the site ranks more highly or not.
craiglist does not penalise but your post on craiglist expires after 3 months. i remember when i submitted my site soon after submission a message arrived tht my listing will expire after 3 months.