AI can drudge up untrustworthy sources or just feel kind of “off,” but the technology has also been pretty consequential for some business owners. In fact, celebrity real estate agent Ryan Serhant said at the Fortune Brainstorm Tech conference last week that ChatGPT nearly blew a $50 million deal for his firm.

When asked by Fortune’s Term Sheet editor Allie Garfinkle about what happens when AI goes wrong, Serhant, the founder and CEO of his namesake brokerage, Serhant, remembered a time when he was selling a New York City penthouse.

It was the kind of trophy asset that’s infamously hard to price because it’s impossible to find comparisons. After what Serhant described as a “contentious” back-and-forth—he likened it to dueling “kings of the world,” with the buyer and the seller each wanting to win—the deal sheet went out at $50 million flat. Then, at the eleventh hour, it nearly died.

That’s because the buyer, Serhant said, went to ChatGPT and typed a version of “I’m looking to buy this, is $50 million too much?” The chatbot said yes.

The buyer’s broker then called Serhant to pull out of the deal because AI said it wasn’t worth it. Unsurprisingly, Serhant’s reaction was pretty blunt, telling the broker the move was “dumb” and “stupid.”