I have made multiple yahoo chat bots, and would be able to create a craigslist auto-responder that would be very efficient and would not get you blocked, I would get around being blocked by using a proxy system, that does not require that you find the proxy servers, they are already located for you, and work flawlessly, my terms are as follows
50% of total project bid up front (negotiable)
The rest of the project will be split up into parts, and I would receive payment after each part is complete and released to you
Project will be completed in no more than 90 days