Still, some sellers don’t get the message right away. “It’s almost like the boyfriend or the girlfriend who stops calling,” said Mr. Willkie of Brown Harris Stevens. “ ‘They didn’t tell me they didn’t like me anymore,’ ” he said, quoting the jilted. “Well, no, but they didn’t call you.” In real estate, he said, “it’s the same thing.”

Loath to resort to discounts, some developers and high-end brokers are quietly ratcheting up commissions and other incentives they offer real estate agents to try to increase sales. The Oosten, a 216-unit condominium in Williamsburg, Brooklyn, which began sales more than a year ago, is offering a $5,000 American Express gift card to brokers who can deliver a signed contract for one of its 78 remaining units, listed for $1.14 million for a one-bedroom to $6.42 million for a six-bedroom penthouse.

In November, 200 East 62nd Street, a 115-unit condominium conversion that began sales earlier last year, introduced a $10,000 broker bonus for one-bedroom deals closed by the end of December, $20,000 for two-bedrooms and $30,000 for three-bedrooms. In Midtown, a new 93-unit condominium at 252 East 57th Street, which topped out in October, began offering brokers a 1 percent commission within 60 days of a signed contract — even if the buyer does not ultimately close. Normally, brokers aren’t paid until a sale officially closes, which can take as long as two years in developments under construction.

“We’re doing this to try to raise awareness among brokers who have not been to the building,” said Steven Rutter, the director of Stribling Marketing Associates, which is handling sales

Despite the increase in price reductions, industry experts say the market remains strong. “If a property is worth $1 million and you ask $1.4 million and reduce it to $1.3 million, it’s not an indication of a problem in the market,” said Mr. Willkie of Brown Harris Stevens. “It’s a problem with overpricing.”

Sales remain robust for the bulk of the market, with competition particularly heated for two-bedrooms, where there are still too few apartments to go around. It’s the high end where sales volume has begun to slow. “We still see interesting things happening, including record-setting prices closing,” said Michael Graves, an associate broker at Douglas Elliman Real Estate. “There just happens to be a lot more uber-luxury product coming to market.” As a result, he said, “buyers are much more patient, and some of the exuberance we saw last year has faded away.”

Over all, 189 apartments were sold for $10 million or more in 2015, down nearly 12 percent from the record 214 in 2014, according to CityRealty, which tracks co-op and condo sales.