"As many as 20 to 30 percent of agents’ high-end listings [in San Francisco] are now totally underground"

ModernLuxury:

That means no advertising, no listing sheets, no email blasts. In place of open houses, sales tactics for these homes include password-protected websites, phone-call-only marketing campaigns, and, as I found out, NDAs.

...

There are pre-IPO tech founders who want to keep speculation about their financial outlook to a minimum; or Sand Hill Road types trying to project an air of modesty. And then there’s that oh-so-Silicon-Valley notion that building a whisper network of potential buyers gives a home a level of intrigue, and buzz, that’s priceless.