Occasionally, a staged apartment looks so good that sellers rethink their decision to move. One of Ms. Kenney’s first projects was an owner-occupied two-bedroom apartment on the Upper West Side. The clients were suburbia bound.

“The apartment wasn’t set up well,” Ms. Kenney said. “Most people aren’t designers; they just do the best they can. We had the sellers take a lot of stuff out, then we rearranged everything and brought in accent pillows and bedding.”

She continued: “And when we got done, they said, ‘This is so great. We’re not going to move.’ And I thought, ‘I am never going to work in this town again!’”

Three months later, the couple decided, on second thought, that they really did need more space.

Mr. Eiden recalled a similar experience, when the owners of a three-bedroom duplex in Chelsea said to him, “Please don’t be mad at us. The apartment looks super great, and we don’t want to sell it.”

He had decluttered their apartment, brought in lighting and a clutch of throw pillows, and rearranged the furniture to better define the space. “I made more than my commission back with all the referrals they’ve given me,” Mr. Eiden said.

But with staging, as with weight-loss products, results may vary.

“I don’t think, in this market, we can guarantee that if you stage you will get X amount more dollars or a bidding war or even the asking price,” said Ms. Larson, of Warburg. “It’s just that this is a buyer’s market with a lot of competition, and we need to check every box we can.”