A woman who worked in the area and had seen the newly posted photos online “asked if she could come and see the house on her lunch hour,” said Ms. Benmen, an associate broker with Coldwell.

After checking out the two-story house, on a manicured and treed quarter-acre lot close to a park, she asked if she could come back with her husband that evening.

Ms. Benmen agreed and promptly canceled her weekly mah-jongg game.

Before the evening meeting, however, the buyer called back with a $790,000 offer, saying, “This is the house we are looking for.” This was last May, and she wanted her son to attend the neighboring E. M. Baker Elementary School in September.

Ms. Benmen suggested that the buyer wait until her husband saw the house, which had an updated kitchen, a fireplace and a detached two-car garage but did not have air-conditioning.

But the buyer, armed with a prequalification for a mortgage and having “done her homework” by scouring other houses in the neighborhood, said she didn’t “want to lose it.” She provided the names and phone numbers of her house inspector and lawyer.

“The house sold in five minutes; the offer was accepted, ” Ms. Benmen said. “It was priced right; it was priced to sell.” If the listing and sales price are close, a home has been priced “right on the money.”

“When there is a huge discrepancy, it just detains” making a sale, she said.

A quick sale may seem like an anomaly in a gloomy market where many homes languish for months, sometimes years. But when the price is set realistically for the market — even a little on the low side — savvy buyers are jumping in, often with competition. A result can be bidding wars and offers that sometimes exceed the listing price.

Last month Barbara Drucker, an associate broker with Prudential Douglas Elliman, listed a four-bedroom Cape with a basement and a garage on an oversized 80-by-100-foot lot in Massapequa Park for $299,999, noting on the listing that the seller would accept cash only.

At the first open house, 20 buyers showed up. Half of them submitted offers. The seller took the highest, $310,000. The sale is scheduled to close next week.

The reason so many made offers in that case was twofold. In addition to the realistic price, Ms. Drucker said, “the location was perfect,” walkable to the village and the train station, and in the Massapequa school district. Though the house was cluttered and such “a disaster” that “you wouldn’t even want to go into the kitchen or the bathroom,” price superseded looks.

“If we price it right, even a little under what the norm would be,” Ms. Drucker said, “we are finding we get better offers, more offers.” She has sold 21 homes this year. “If we price it over at all, people give us lowball offers.”

Jonathan J. Miller, a real estate appraiser who is the president and chief executive of Miller Samuel Inc., said that through September of this year, 1 percent of sales in Nassau County occurred within two days, down from 1.2 percent in 2010 when the “federal home buyer tax credit pushed demand and reduced marketing times.”

The properties that sold in zero to two days this year were an average of 37.7 percent higher-priced than the overall market, he said. Last year, such sales were 122.8 percent above the overall market.

To seal a deal quickly on David and Marissa Kahen’s five-bedroom farm ranch in Roslyn Heights last month, Michelle Cohen, an executive vice president and associate broker at Laffey Fine Homes, took what she called an “auction approach” and created “an old-fashioned bidding war.”