On March 1, New York real-estate agent Peter Ocean thought he had reason to celebrate: His clients accepted an offer of $10.25 million for their four-bedroom co-op in Lenox Hill, which had been on and off the market for more than a year, last asking $10.5 million. 

Days before the planned contract signing, the buyers even came back to purchase some of the furniture. “They weren’t even going to paint,” Ocean said.