What has Google actually said about local ranking?
Google's help pages say local results are based mainly on three things: relevance, distance and prominence. Relevance is how well a profile matches the search. Distance is how far the business is from the searcher or the place named in the search. Prominence is how well known the business is, and Google says it draws on information from across the web, including links, articles and directories.
Google also states that it does not accept payment to improve a business's local ranking. What Google has not said is that a link pointing at a Maps listing address is a ranking input of its own. That gap is the honest starting point for any plan.

