Publicis Groupe told clients this month to stop using The Trade Desk. The Trade Desk's CEO fired back on LinkedIn, accusing agencies of running from transparency while arbitraging programmatic. The press releases used words like "partnership values" and "audit rights."
Here's what actually happened: the holding companies have spent nearly a decade rebuilding the exact rebate economics that the ANA exposed in 2016, and the new packaging is finally tearing at the seams.
The billion-dollar memo nobody was supposed to see
In November 2025, a former WPP executive named Richard Foster filed a wrongful termination lawsuit seeking more than $100 million in damages. Foster, who served as CEO of Motion Content Group, alleged he was fired after raising objections to WPP's media rebate practices. That's a story in itself.
But the real gift came in WPP's counter-filing, which made public a 2024 memo Foster had authored. According to the memo, GroupM exceeded $1 billion in global net sales for what WPP internally calls "non-product related income" in 2023. That's WPP's sanitized label for principal-based media revenue. The memo also referred to the practice as "proprietary media trading" and "purchase risk media deals," depending on which internal audience needed convincing.
The memo projected that revenue line would grow 15% in 2024, even while WPP's overall net revenue was slightly declining. Let that land for a second: the fastest-growing revenue stream inside one of the world's largest agency holding companies is money made by buying media wholesale and marking it up to clients.
Same game, different decade
If this sounds familiar, it should. In June 2016, the Association of National Advertisers and auditing firm K2 Intelligence published a report documenting pervasive cash rebate practices across US media buying. Agencies were collecting kickbacks from media sellers based on spend volume, and those refunds never made it back to clients. The industry collectively gasped, promised reform, and then quietly moved on.
Direct rebates are still technically prohibited in the US, same as they were a decade ago. They remain commonplace in Europe, where nobody pretends otherwise. But American holding companies found a workaround: principal-based trading. The agency buys inventory on its own balance sheet at wholesale rates, marks it up, sells it to clients, and pockets the spread. It's not a rebate. It's a "media investment product."
The incentive structure is identical to what K2 documented. The money flows the same direction. The only thing that changed is the paperwork.
The numbers everyone pretends not to know
Here's where following the money gets interesting.
WPP's principal media revenue crossed $1 billion in 2023, according to Foster's memo. We only know this because of a lawsuit. WPP does not voluntarily disclose the figure.
