Court filings in the Richard Foster lawsuit reveal just how much GroupM controlled—and how little of that money allegedly flowed transparently to clients.

Sometimes the most damning evidence isn't an accusation. It's a spreadsheet.

Buried in the ongoing lawsuit between former GroupM executive Richard Foster and WPP is a set of internal documents that paint a remarkably detailed picture of how the world's largest media buying operation actually makes money. Whatever the court eventually decides about Foster's specific claims, the numbers themselves tell a story worth understanding.

The Scale of the Machine

At its peak, GroupM controlled roughly $60 billion in annual client advertising spend. That gave it between 20% and 50% market share across key global markets. Scale is power in media buying—the more client money you aggregate, the better deals you can extract from media vendors.

But here's where it gets interesting. According to a 2019 internal presentation dubbed "Project Claridges," GroupM generated approximately $1 billion annually in what it called "non-product related income." This included rebates, services, and something called "purchase risk inventory"—proprietary deals where the agency buys media in bulk and resells it to clients.

The internal target? Grow that income line by 15% year-over-year.

The Opt-In Problem

Foster's lawsuit alleges that much of this income never flowed through to clients who had contractually opted out of rebate arrangements. The internal documents now in the public record offer some supporting texture.

Looking at GroupM's top 30 U.S. billing clients in 2023—accounting for $13.4 billion in total spend—the numbers are striking. Of available proprietary inventory and rebate deals (classified internally as "Green" and "Red" billings), 97.4% went unused by opted-in clients.

Google, GroupM's largest U.S. client at $2.3 billion in billings, used just 0.51% of available proprietary inventory. Among the top 10 clients (excluding Google), usage rose slightly to 15%, with 91.9% of proprietary deals going unused.

What happened to that unused inventory? That's the $3-4 billion question Foster says he raised—and the question that allegedly got him pushed out.

The Platform Concentration

The filings also reveal just how much of GroupM's global buying was concentrated among a handful of platforms. In 2023:

  • Google: $9.4 billion global, $4.9 billion U.S.
  • Meta: $3.7 billion global, $1.4 billion U.S.
  • Amazon: $1.1 billion global, $773 million U.S.
  • TikTok: $1.1 billion global, $459 million U.S.
  • The Trade Desk: $1.1 billion global, $884 million U.S.

That's $18.5 billion flowing through just a handful of tech platforms globally. The leverage this gives GroupM in negotiations is enormous. The question is who benefits from that leverage—and how much of it gets passed through versus retained.

The TikTok Experiment

One of the more interesting exhibits is a pilot partnership Foster's Motion Content Group ran with TikTok in the U.S. market. Unlike GroupM's traditional deals, this one was structured as a transparent co-investment arrangement.

Over 14 months across four deals, Motion invested $69.7 million and generated $106.7 million in ad credits—yielding $28.8 million in net sales. The projected profit: roughly $30 million from a single platform partnership, with full transparency on the deal structure.

Foster's proposal to scale this model projected net sales of over $2 billion by 2029 at profit margins above 70%. WPP declined to pursue it. Foster alleges he was fired for pushing too hard on transparency. WPP says he was let go for unrelated performance issues.

What the Numbers Don't Say

Nothing in these documents proves wrongdoing. Rebate structures in media buying have been legal and common for decades, though their transparency has been a persistent industry controversy. The ANA's landmark 2016 investigation into agency practices raised many of the same concerns, leading to widespread contract renegotiations but little structural change.

What the numbers do show is the sheer magnitude of what's at stake. When $60 billion flows through a single organization, even small percentage variations in how that money is handled amount to hundreds of millions of dollars annually.

The lawsuit continues. But for anyone wondering how media agencies really make money—beyond the fees clients think they're paying—the court filings offer a rare window into the machine.