Hi, this info I pulled out from Google Support,
Hope it helps:
Ranking of Google Places listings
Google Maps search results are based primarily on relevance, distance, and prominence. These factors are combined to help us find the best match for your search. For example, our search technology might decide that a business that's farther away from your location is more likely to have what you're looking for than a business that's closer. Here's more detail on what relevance, distance, and prominence mean:
Relevance: Relevance is how well a local listing matches what someone is searching for. A complete and detailed listing in Places can help us better understand your business and match you to relevant search results.
Distance: Just like it sounds -- how far is each potential search result from the location term used in a search? If you don't specify a location in your search, we'll calculate distance based on what we know about your location.
Prominence: This describes how well-known or prominent a listing can be. This is based on information we have about a business from across the web (like links, articles, and directories). Some places are more prominent in the offline world, and we try to reflect this online as well. For example, famous museums, landmark hotels, or well-known store brands that are familiar to many people are also likely to be more prominent in search results.
Google Maps and Google Places are free services, so there's no way to request or pay for a better ranking. In addition, we do our best to keep the details of the algorithm confidential in order to make the ranking system as fair as possible for everyone.
Thanks,
Russel