Realtors say sales of single-family homes in Maine have increased by 21 percent between January 2012 and the same month this year. Statistics released by a statewide multiple listing service show 664 homes changed hands last month, compared to 547 in January 2012. The median sales price for those homes reached $162,000, a rise of 3 percent from a year earlier. The median indicates that half of the homes were sold for more and half sold for less. Maine Association of Realtors President Bart Stevens says Maine is shifting from a strong buyer’s market to a more balanced market.