More and more sites are promoting themselves as one stop data entry mega sites promising your ad will go "everywhere", including ebay and craigslist.  If this were possible (and legal) that would be nice and we would do that too. 

From Craigslist's own policy: 

"It is expressly prohibited to post content to craigslist using anyautomated means. Users must post all content personally and manuallythrough all steps of the posting process. It is also expressly prohibited forany user to develop, offer, market, sell, distribute or provide an automatedmeans to perform any step of the posting process (in whole or in part). Anyuser who develops, offers, markets, sells, distributes or provides an automatedmeans to perform any step of the posting process (in whole or in part) shall beresponsible and liable to CL for each instance of access to craigslist (by anyuser or other third party) using that automated means."