Sony Pictures ran its own investigation into WPP's media buying arm. It did not like what it found.

An amended complaint filed last week in Foster v. WPP lays out, in granular detail, what Sony's investigators say they uncovered inside GroupM (now rebranded WPP Media): a system for routing client rebate money back into WPP's own margin, dressed up as a media discount. In China alone, Sony's probe put the number at $350 million retained by WPP against $110 million passed through to clients. The complaint alleges the mechanics "proliferated across other markets."

WPP calls the amended complaint "baseless." A court will eventually decide that. But the document itself, and the criminal case that preceded it, are now both part of the public record, and they tell a fairly specific story about what happens when the entity auditing your media spend is the same entity spending it.

Former GroupM executive Richard Foster sued the company last November, claiming he was fired for raising the alarm on what he described as an unlawful rebate scheme, one where money that contractually belonged to clients was quietly kept by the agency instead. That was the original complaint. It was, by design, one man's account.

The amended complaint is different. It's built on someone else's audit: Sony's own.

According to Foster's filing, Sony's investigators zeroed in on something called "Proprietary Media," or PM/Programmatic, as the primary channel for moving rebate money. The complaint describes it this way: WPP advertises a discount on inventory, but the "discount" isn't really a discount at all. WPP pays a fraction of what the inventory actually costs, covers the rest using money pulled from the rebate pool that was supposed to go to clients, and pockets the spread as "near pure profit shielded from audits."

That's not a rounding error in a media plan. That's a structure. And per the complaint, Sony backed its findings with contract language on rebate policy, transaction-level financial data, internal WPP emails discussing rebate amounts, and WPP's own tracking systems.

The complaint also states that when Sony's team pressed WPP representatives on how the 80% discounts on some media were actually funded, given that the money traced back to undisclosed rebates, the WPP side reportedly said they had no answer to give, because they did not want to know the answer.

None of this is happening in a vacuum. In 2023, Chinese authorities opened a probe into "rebate mismanagement" inside GroupM's China operation. That investigation concluded last month with Di Fei, GroupM China's former chief investment officer, sentenced to life in prison for his role in a bribery and kickback scandal. Several other employees received lighter sentences. Fei is appealing. WPP maintains it was not a party to the criminal proceeding and cooperated fully throughout.

Sony's investigation, as described in Foster's filing, runs parallel to that criminal case and lands on a similar number: roughly $460 million in China rebates, with $350 million staying at WPP and $110 million reaching clients. The complaint's framing is blunt: the China scheme wasn't an isolated local failure. It was "a lever to artificially inflate earnings at WPP" more broadly.

The most damaging line in the complaint isn't about the money. It's about who inside WPP already knew the risk.

Foster alleges that when he raised GroupM Trading's rebate practices directly with Nicola McCormick, WPP's general counsel and a former GroupM general counsel herself, she described the exposure in a single word: "existential."

That's a lawyer's word, not an accountant's. It suggests the concern inside the building wasn't whether the practice was aggressive. It was whether the company could survive what happens if it comes out.

Long before Sony's investigators went looking, Jared Belsky was already saying the quiet part on his own record.

Belsky, CEO of the independent agency Acadia and a former CEO at 360i, told ADOTAT that unreported rebates pad agency margins by up to $40 billion industry-wide, a figure he's put in writing before. Asked to explain the mechanics, he didn't hedge: "You don't get to double and triple, quadruple dip, and then say you're a trusted advisor." He called the practice, plainly, unacceptable, deplorable, and borderline fraudulent, and named the same two mechanisms at the center of the Foster complaint, rebate retention and principal-based media trading, as the two that bother him most.

Belsky's not just a critic from the sidelines. He told ADOTAT that Acadia ran a one-time rebate experiment in 2026, took the money, and redistributed it back to clients pro rata, specifically because he couldn't justify keeping it. His broader argument is that the entire practice survives on client ignorance: "CMOs and marketers generally don't understand the problem. And if they understood the problem, I think they would be more passionate about why it would rub them the wrong way."

The origin of the practice, he says, traces back decades to linear TV and radio trading, where small shops genuinely took on principal risk and disclosed it. What changed, in his telling, is scale: "as the big old cos especially have made this practice acceptable... it's just gotten uglier and uglier." Even Michael Farmer, the agency-compensation researcher whose books first quantified how far agency economics have drifted from client interests, came up unprompted in the conversation as the person who should be tracing exactly when and where this started.

Sony isn't the first outside party to look at GroupM's rebate math and land on a figure that dwarfs what the company has ever disclosed.

Nick Manning, the former Ebiquity chief strategy officer who co-founded Manning Gottlieb OMD, published his own analysis of the underlying "Project Claridges" document back in the spring, before Sony's findings ever surfaced in a court filing. His number: GroupM generated roughly $1 billion in 2023 from principal media trading, more than half of WPP's total profit that year. He also found that only a third of WPP's ten largest clients had even opted into the practice, and that the clients who did opt in saw, in his words, virtually no benefit from doing so.

Manning has a stake in how this reads. He was retained by Foster's legal team, Brewer, Attorneys & Counselors, as a paid expert witness, and he's said so publicly himself. That's a disclosed conflict, not a hidden one, and it doesn't make his math wrong, but it does mean his numbers arrive with a side.

Months before the Sony allegations, Manning was already describing the underlying dynamic on a K2 Report retrospective panel: an agency answering to two masters at once. "You have a situation where the agency that you see day to day has two bosses," he said. "The people behind the agency [and] the people who are pulling those strings in the holding company groups... it's very difficult to serve two masters equally."

Sony's investigators, per Foster's complaint, arrived at a version of the same conclusion through forensic accounting rather than industry commentary. The fact that an outside analyst and an outside investigator landed in the same place, independently, using different methods, is the part of this story that doesn't depend on how the lawsuit resolves.

The amended complaint arrives just ahead of a hearing on WPP's motion to dismiss the case, which is likely not a coincidence. Foster is seeking $100 million in damages. WPP will file an updated motion to dismiss.

A WPP spokesperson gave ADOTAT the following statement:

"This amended complaint, filed just prior to the hearing, is an attempt to avoid its dismissal. Both complaints are baseless and without merit, and WPP will be re-filing an updated motion to dismiss. We have confidence that this matter will be resolved through due legal process."

While the amended complaint moves through discovery, WPP's own leadership has been floating a different story about how to rebuild client trust: outcome-based pricing, agency pay tied to results instead of fees or spend. WPP Media CEO Cindy Rose has said that shift is coming, even if she's characterized it as still years away.

Michael Farmer, the agency-compensation researcher and author of Madison Avenue Manslaughter, isn't buying it, and made the case directly to ADOTAT.

His argument starts with growth, not fees. Forty of the top 60 advertisers in the world have grown at roughly half the rate of nominal GDP for the past 15 years, he said, and that stagnation is what pushes marketers toward "low cost everything," cheap programmatic media and squeezed agency fees. Agencies, in his telling, have never actually measured or documented the work they do, which leaves them, in his words, "in no position today to up their game and now commit to improved outcomes."

His sharper point is about who gets to define "outcome." The measures Meta, Google, and Amazon have touted in the past, he said, have never actually been about improved sales. And history isn't on the holding companies' side either: "The shift to programmatic around 2009 did not drive brand growth. Quite the opposite."

His prediction: "Outcome-based pricing will turn out to be a complete disaster if agencies do not get involved in designing the outputs and charging for them." That's effectively the same failure mode as the rebate scheme Sony says it found: a system where the party being measured also writes the measurement, and the client is left trusting a number it has no way to independently check.

That's the throughline underneath both stories. Whether the mechanism is a hidden rebate pool or an outcome metric nobody outside the holding company gets to define, the entity setting the scorecard and the entity being graded on it keep turning out to be the same company.

Strip away the china sentencing and the litigation and what's left is a structural problem that predates this lawsuit by years: nobody outside the agency can actually audit the fee stack they're paying into.

Alessandro De Zanche, the sell-side columnist at AdExchanger, has been making this point for months, and it applies almost too neatly here. "A disclosed fee is still unauditable when the entity charging it is anonymous or unverifiable," he told ADOTAT. "An audit needs a name, directors, a registered address." Sony had all three, a global media company's legal and forensic resources, contract language, transaction-level data, internal emails, and it still took an independent investigation to surface what Foster says WPP's own general counsel already knew.

De Zanche's broader argument is that transparency doesn't arrive through technology, it arrives through human intervention, someone with the standing and the incentive to actually look. "In a functioning market, following the money is bookkeeping," he said. "Here, it is a forensic project." The Foster complaint is, almost literally, that forensic project: a client big enough to run its own investigation, finding what a normal audit clause never would have caught.

Most advertisers are not Sony Pictures. Most don't have the leverage, or the legal budget, to commission their own probe into their agency's rebate mechanics. That's the part of this story that survives the lawsuit regardless of how the motion to dismiss shakes out.

How we reported this: Built primarily on Richard Foster's amended complaint in Foster v. WPP, New York State Supreme Court, filed Aug. 13, 2026, reviewed via the public court docket and cross-referenced against Chinese court reporting on the Di Fei sentencing and prior coverage of the 2023 GroupM China rebate probe; WPP was contacted before publication and its full statement is included above.

Additional context comes from Alessandro De Zanche, interviewed on the record for a separate ADOTAT investigation into fee-stack disclosure; Nick Manning, whose figures and quotes come from his own published analysis (MediaCat UK, May 2026) and a June 2026 Digiday panel, and who is a retained paid expert witness for Foster's legal team, a disclosed conflict; Jared Belsky, quoted from his own on-record interview on The ADOTAT Show (an appearance also disclosed here), from an auto-generated transcript not independently re-verified against tape; and Michael Farmer, whose comments were sent directly to ADOTAT by email and reproduced with permission. Dollar figures cited ($350M, $110M, $100M in damages) are as stated in the court filing, not independently audited by ADOTAT. ADOTAT has no financial relationship with WPP, GroupM, WPP Media, or Sony Pictures, and no subject was given advance review beyond the standard right-of-reply request described above.