Local SEO campaign can help a business achieve great results by narrowing the ad exposure to the very specifics of certain cities or distance from a point of address. Having a consistant & optimize local listings by listings in Google Local (Places), Microsoft Bing Local, Yahoo Local, Yelp, YellowPages & wide range of other priminant local directories. You will need a physical address to nbe able to verify existance but there is an option to specifiy a service location list and hide the actual address number and street. P.O Box do not work that well.
Local campaigns can include a sponsored reach via Google AdWords, Microsoft Bing Local which also includes Yahoo Local.