Make sure to follow the rules and not be overbearing on the sites. But you can simply create a FREE opt in page with Google Forms (Watch Video) but you can also get a service that does this we well like EZ Lead Pages. This way costs money but is more refined but the results should be better as well since it is more focused. Finally, when you do have a listing to market using List Reports is a great way to put a text for info ad out there. Place that in FB and Craigslist, then when it comes in ad to your CRM.