Google Local works based on citations and the more citations you have the higher your listing will rank. A citation is basically a mention of your business address of phone number on a website that Google trusts as a data provider.
The standard advice is to list your website in as many of the major citation providers as possible which is a good strategy until all your competitors do the same thing. Citation building is the same as link-building, you need to get the sort of citations that your competitors can’t get.
One of the best ways to do this is to build a custom relationship with a partner which is trusted by Google to give citation data but in a sector not directly related to yours. As an example if you had a chain of restaurants you could approach a hotel reviews website and pay for a sponsored section on each of their city & town pages listing the 3 nearest restaurants from your chain.
The best way to demonstrate this is to show an example of how Halfords citations are being pulled from the excellent ukcampsite.co.uk website. The site has a very useful feature where it shows the nearest Halfords to each campsite so that caravan owners can buy spare parts etc.
If you have a look at the place page for Halfords you can see that Google is pulling all of the data from the source site into the Halfords listing as a citation.
Now obviously Halfords and ukcampsite.co.uk are not intentionally trying to do this to get citations, they have a very useful feature and Google is misinterpreting the page data.
However I’m sure you can see how there is a lot of potential for this to be intentionally abused by people who are willing to pay websites purely to get lots of valuable citations.