Update July 2014: If you are looking to convert a Brand page to a Local page Google has recently released that functionality. Read about it here: Google Now Allows Brand Pages to Become Google+ Local Pages
Because of the slow and never ending transition of Places to Plus and because of less than stellar communications from Google since the rollout of Plus, a very large number of small local businesses have ended up with more than one Google+ Page.
Over the past 6 weeks I have received a stead stream of inquiries as to how to deal with the situation. I wrote up my answer today at LocalU.How Do I Merge Two Google+ Page Pages? A Very Common Question by Mike Blumenthal