Observed Signal · Mar 25, 2026 · Legal case / Industry investigation · Source: Digiday · Impact: 3/5 · Sentiment: Negative
Nick Manning: Principal Media Is Anti‑Marketer
Digiday interviewed media consultant Nick Manning about documents from an ongoing court case (the “Foster Papers”) that shed light on agency principal‑media buying practices. Manning, a former CEO of OMD U.K. and chief strategy officer at Ebiquity, argues principal media — where agencies pool client spend to buy inventory and resell it at a markup — creates conflicts of interest, two tiers of clients, and reduced transparency. The article cites industry research (ANA) showing increased use of principal buying by some advertisers and widespread client concern about transparency. Manning is serving as an expert witness for Richard Foster and suggests WPP/GroupM’s alleged principal practices undermine client trust and could complicate WPP’s new strategy under CEO Cindy Rose. WPP disputes the characterization, saying the papers reflect a rejected business proposal.
Reveals alleged nontransparent principal‑buying agency practices at a major holding company (WPP/GroupM), raising client trust concerns and adding momentum to industry scrutiny from trade bodies and research firms.
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Key Takeaways & Evidence Grounding
- Documents published during the WPP v. Richard Foster court case are referred to as the “Foster Papers.”
- Nick Manning is a media consultant, former CEO of OMD U.K. and former chief strategy officer at Ebiquity; he is retained as an expert witness by Foster’s lawyers.
- Principal media buying involves agencies combining client investments to obtain discounted inventory and reselling it to clients at a markup.
- 37% of U.S. advertisers said they had increased their use of principal media in the last year, according to the ANA (as cited in the article).
- The article notes industry scrutiny from Forrester and ISBA and a public dispute between Publicis Groupe and The Trade Desk; it also mentions Meta began striking principal media deals with agencies in 2025.
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Principal Media's Rise: Agencies Face a New Reality
The article analyzes how global ad holding companies are expanding principal-based media trading—where agencies buy media on their own books and monetize the spread—creating a multibillion-dollar revenue stream that can misalign agency and client incentives. It traces the issue from historical rebate controversies through recent disclosures in Foster v. WPP, where a 2024 memo revealed GroupM’s "non-product-related income" exceeded $1 billion in 2023 and was forecast to grow. The Trade Desk publicly criticized principal-based practices and agency transparency, while industry bodies like the ANA urge marketers to understand benefits, risks and governance needs. Executives quoted (Publicis, WPP, Omnicom) acknowledge principal media exists but differ on strategic emphasis. The piece warns the mechanics will evolve but the incentives for holdcos to pursue high-margin principal revenues are likely to persist.
Principal Media Buying Reshapes Agency Economics
Principal media buying — agencies purchasing and reselling media inventory — has moved from a niche, behind-the-scenes practice to a central and public driver of agency economics. Proponents cite cost efficiency (often 10–15% savings versus open-market buys) and the ability to subsidize other agency services or reinvest profits into capabilities like AI and data infrastructure. Critics highlight opaque pricing, undisclosed margins and conflicts of interest that can erode trust; the ANA reports only 57% of marketers have governance rules for the practice. As procurement and consultants emphasize cost savings, agencies with scaled principal operations gain a structural advantage. The practice is likely to accelerate, but some independents are evolving toward greater transparency (margin disclosure, opt-in models, comparative buy analysis). The article argues clients should prioritize outcomes and media quality, not just cost extraction.
Google Antitrust Ruling Spares Ad Stack, Pressures Trade Desk
A federal judge ruled that Google must open up its ad exchange and publisher ad server to more competition but stopped short of forcing a breakup of its adtech stack. The remedies include connecting AdX and DFP to Prebid, requiring equal terms for AdX bids on alternative servers, curbing self-preferencing, and sharing auction data. For The Trade Desk, which has positioned itself as the neutral alternative to Google's walled gardens, this outcome weakens its core pitch: a fairer and more transparent auction reduces the urgency for publishers to seek alternatives like OpenPath. The article also notes that Google's decision to keep third-party cookies has already slowed adoption of alternative IDs like UID2.0. Analysts suggest The Trade Desk's narrative is shifting towards CTV and agentic advertising as the open-web competition with Google evolves.
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