1 of 3 condos recently sold in Manhattan sold at a loss according to luxury real estate firm Brown Harris Stevens. Over the past 10 years, condo values across New York City have grown 16%, while many other major cities saw higher price growth, according to Zillow data on condominiums and co-ops. Experts point to shrinking demand and slow real estate activity across the country. The Manhattan market also saw less foreign investment in all-cash purchases of residential real estate.