I just checked the CL's terms of use and it explicitly mentions any automated posting to be illegal. So, if it is a generic commercial idea you wish to scale up, note that:
It is expressly prohibited to post content to craigslist using any automated means. Users must post all content personally and manually through all steps of the posting process. It is also expressly prohibited for any user to develop, offer, market, sell, distribute or provide an automated means to perform any step of the posting process (in whole or in part). Any user who develops, offers, markets, sells, distributes or provides an automated means to perform any step of the posting process (in whole or in part) shall be responsible and liable to CL for each instance of access to craigslist (by any user or other third party) using that automated means.
