While many of those early viewers were younger and couldn't afford the multimillion-dollar apartments on the show, "buyers are influenced by the kids," Serhant said.

Serhant launched his own agency in 2020, training agents to produce videos, boost their social media followers and grow their personal brands. Last year, the firm saw over $2 billion in sales and 35% growth in its number of agents.

"I want our agents to be able to do deals everywhere, to anyone, on any platform," he said.

But Freedman said experience with negotiating deals, relationships developed over time and deep knowledge about neighborhoods and buildings remain the cornerstones of selling real estate.

"We sell real estate, not technology," Freedman said. "We work hard."

Disclosure: CNBC parent NBCUniversal owns Bravo.