In many cases, Mr. Malin added, clients might be coming to New York for the first time and might not have a social network. Then the real estate agent who is their first contact in the city could easily become more than the person who found them a place to hang their hat.

“I like to say that being in the real estate business is like being in the hospitality business,” Mr. Malin continued. An agent might introduce a client to a neighborhood, suggest restaurants and become a resource, he said. The next step might involve inviting the client out to dinner as a gift after the deal has been completed, or inviting the client to a party the agent is having.

“You’ve spent a lot of time together,” he said. “You’ve shared a lot of information. And all of a sudden you realize you have a lot of things in common, and one thing leads to another.”

Sometimes, the thing it leads to is a breakup.

It had been a late night for Joanna Mayfield Marks, an associate broker at Halstead Property. At 11 p.m. or so, she accepted her boyfriend’s marriage proposal. That’s why she was half an hour late for an appointment the next day to show several Manhattan apartments to an artist who was relocating from Buffalo.

“I could tell pretty soon that he wasn’t going to want to rent from me, because he kept talking about wanting to live in Brooklyn, where all the artists lived,” said Ms. Marks, who is now 43. Despite the fact that the morning had been a bust, she was suddenly feeling butterflies (but she had just gotten engaged), and all because of this cute guy (did we mention that she had just gotten engaged?).

Ms. Marks, the sort who reflexively puts it all out there, put it all out there within 20 minutes of meeting this new client, the artist.

“I think I made a terrible mistake,” she announced to him. “I got engaged last night.” He listened without comment.