A version of this article first appeared in CNBC’s Inside Wealth newsletter with Robert Frank, a weekly guide to the high-net-worth investor and consumer. Sign up to receive future editions straight to your inbox.

The wealthy are increasingly embracing the concept of "quiet wealth," opting for private purchases of mansions, art, and classic cars to maintain discretion and privacy. Auction companies and luxury real estate brokers have noted a significant shift towards private sales and off-market listings, as affluent buyers and sellers seek to avoid the scrutiny of social media and public attention.

Despite a 19% decline in public auction sales last year for major auction houses like Sotheby’s, Christie’s, and Phillips, private sales have shown resilience. Sotheby’s saw a 4% increase in private sales, while Christie’s experienced a 5% rise, with both houses collectively handling $2.4 billion in such transactions. Notably, CNBC reported that hedge-fund billionaire Ken Griffin privately acquired a Mark Rothko painting for over $100 million, highlighting the growing trend of private dealings even as public auctions wane.

The classic car market has also seen a substantial shift towards private sales, especially for high-value models. RM Sotheby’s, a prominent classic-car auction house, has witnessed its private sales division's revenue quadruple over the past four years. Shelby Myers, global head of private sales for RM Sotheby’s, emphasized the growing preference for private transactions, noting, “Discretion today is key. People can buy without the whole world staring at them.” Private sales now constitute nearly a third of RM Sotheby’s revenue.

The rise in private sales across various markets is largely driven by social media, technological advancements, and cooling prices for collectibles. Public auction results are widely disseminated online, leading sellers to prefer private deals to avoid the risk of public failure. Myers explained, “It’s very public now when someone loses money on a sale, and no one wants that. Up until a few years ago, you could buy a car at auction and the prices wouldn’t be splattered all over social media.”

In the real estate sector, many of the most significant deals in prime locations like Manhattan, Malibu, Aspen, the Hamptons, and Palm Beach are increasingly conducted off-market. These "whisper" or "pocket" listings involve properties that are not publicly advertised but are quietly marketed among a select group of brokers and potential buyers. For instance, a townhouse in Manhattan’s Greenwich Village recently sold off-market for $72.5 million, setting a record for downtown townhouses. Similarly, a 13,000-square-foot mansion in Palm Beach was sold off-market for $60 million, one of the highest prices for a non-waterfront property on the island. In Aspen, the first-ever sale exceeding $100 million—Patrick Dovigi's mansion on Red Mountain to billionaires Steve Wynn and Thomas Peterffy—was also an off-market transaction.

The trend towards off-market deals, which began in Los Angeles during the 1980s and 1990s with celebrities seeking to avoid public exposure, has now expanded to include wealthy but not necessarily famous sellers. Douglas Elliman real estate agent Ernie Carswell noted that even average multi-millionaires or billionaires now prefer the privacy of off-market sales. He recounted working with a billionaire client in New York seeking a special property in Los Angeles, currently negotiating an off-market deal for a mega-mansion owned by a Middle Eastern billionaire.

Carswell emphasized the importance of broker relationships in these private transactions. He mentioned that for properties under $5 million, off-market listings are less practical due to the larger potential buyer pool and the benefits of broader marketing. However, for luxury homes priced over $20 million, the limited buyer pool and the existing broker network make off-market sales more viable. “Never before has the need for a skilled, connected real estate professional been more valuable, especially at the high end,” he stated.

Despite the advantages of privacy and discretion, some brokers argue that private sales might result in sellers missing out on the highest possible price. Real estate broker Noble Black of Douglas Elliman pointed out, “They’re leaving money on the table. There is a valid reason for not listing, you want privacy and discretion. But you’re paying a premium for that.”