The Digiday Podcast: After WPP Reckoning — The Case For and Against Principal Media (March 17, 2026)

Main Theme:
This episode delves deep into the ongoing debate surrounding "principal media buying"—a controversial ad buying practice whereby agencies purchase digital media inventory for themselves (often at a discount or with rebates), mark it up, and then resell it to clients. Triggered by a new wave of documents from the WPP whistleblower case, the discussion explores the ethical, operational, and competitive dimensions of this practice as it stands in 2026, a full decade after the original ANA transparency report brought agency kickbacks and rebates to industry-wide attention.

Key Discussion Points & Insights

1. Principal Media: What's Old Is New Again

• Despite years of scrutiny, the practice of principal media buying is as relevant as ever due to recent high-profile events at WPP, new transparency debates, and public commentary from independent agency leaders.
• Core Question: Is principal media buying a necessary cost of doing business for agencies, or an underhanded way to obscure rebates and markups from clients?
• Quote: "You could call it either marketers recurring nightmare or matter of deja vu... we are indeed once again talking about it 10 years afterwards." – Tim Peterson [01:25]

2. Defining Principal Media (and All the Synonyms)

• Michael Burgi clarifies terms: Principal media, principal buying, and principal trading all describe agencies directly buying advertising inventory (often receiving rebates or lower rates), then reselling (marked up) to clients.
• The biggest issue is opacity—holding companies' financial reports use vague terminology and make it hard for clients to track what’s happening with their budgets.
• Agencies argue that, with client procurement squeezing margins, these practices offset revenue loss—but critics call the lack of clarity "a pretty terrible way to make money."
• Quote: "If you boil it down to its essence, principal media is essentially agencies negotiating and buying inventory directly from publishers... then put their clients into it at a markup." – Michael Burgi [07:52]

3. Why Now? WPP’s Lawsuit and Market Evolution

• Seb Joseph: Detailed internal WPP memos (from exec Richard Foster) surfaced in legal filings, laying out the specifics of the agency’s principal media practices—dollar values, percentages, and terminology (e.g., "non product related income" for kickbacks/rebates).
• These new disclosures illuminate just how much agency profit comes from volume-driven rebates, with numbers showing extremely low client uptake on inventory procured via these deals (e.g., 97.4% of proprietary inventory was unused by top clients).
• This puts renewed focus on whether clients are truly benefiting or left in the dark about value flowing to agencies.
• Quote: "97.4% of the kind of proprietary inventory that was being bought on their dime was going unused." – Seb Joseph [15:00]

4. Cases For and Against Principal Media

• For:
  • Agencies undertake risk and provide clients access to inventory (especially in volatile markets); principal buying can sometimes get clients better rates.
  • Agencies argue clients would have to pay them more if this revenue stream were cut.
  • If handled transparently—i.e., "We’re buying, this is what we’re marking up"—many clients may not care.
• Against:
  • The lack of straightforward disclosure opens the door to conflict of interest and undermines trust.
  • Clients may not know if they're paying a fair price or if their agencies are pocketing value meant for the client.
  • Transparency varies—sometimes all a client cares about is outcome, other times CFOs may demand granular accounting.
• Quote: "With principal media, the agency is buying that media inventory for itself first. Right. And then it resells it to clients. So it's almost inverting that sort of brokerage model..." – Seb Joseph [19:04]

5. Agency vs. Supplier: A Blurring of Roles

• With principal buying, agencies are no longer a neutral agent for client interests. Instead, they act as both advisor and seller—a "slippery slope" for trust and performance.
• Quote: "It does call into question the term agency anymore because they are no longer acting as agents." – Michael Burgi [20:23]

6. Competitive Dynamics: Scale, Transparency, and Independent vs. HoldCo

• Larger holding companies can command deeper discounts (and greater profits) from bulk buys; smaller indie agencies lack scale but can claim more transparency as a differentiator.
• The current trend: marketers may talk up transparency in public, but in practice, many are outcome-driven and indifferent as long as return on ad spend is visible.
• Quote: "Marketers kind of don't give a shit as long as they're getting what they need. And a lot of the complaints around this sometimes feels like more kabuki theater than actual concern." – Michael Burgi [30:19]

7. Principal Media in Broader Context: TV Upfronts, Google/Meta, and "Agency as Store"

• The line between upfront TV commitments and principal buying blurs: agencies sometimes buy inventory directly, taking on risk, then parcel to clients.
• Comparison to retail: just like grocery stores, agencies buy in bulk and consumers (brands) rarely know the supplier price.
• Principal media is mirrored by platform offerings like Google’s Performance Max and Meta’s Advantage Plus, where platforms, not agencies, "become the principal."
• Quote: "We haven't talked about the ultimate version of principal media in my mind, which is Google's Performance Max and Meta's Advantage Plus... Ultimately those are principal media products." – Tim Peterson [29:54]

8. The Transparency Debate: How Much Is Enough?

• Full transparency (e.g., disclosing markups/rebates line by line) is rare and possibly unrealistic; many clients trust outcome-based performance and contract guardrails.
• The real risk: if top-level brand finance execs become aware of undisclosed markups, it could reignite backlash (see: 2016).
• Importance of clear contracts: setting up deterrents and consequences for agency bad behavior is key.
• Quote: "CMOs have to decide also how much is enough, because... at some point you just sort of have to trust that your agency is going to do the thing that you've asked them to do and trust that the contractual stipulations are tight enough... " – Seb Joseph [35:46]

9. Future Outlook: A More Mature, Guardrail-Heavy System

• The hosts and guests predict a natural evolution: agencies and marketers will settle into a more regulated, mutually acceptable equilibrium, with principal media not going away but managed with tighter controls and understood risks.

Notable Quotes & Memorable Moments

• "Sup Bergi, welcome back to the show." – Tim Peterson to Michael Burgi and Seb Joseph, setting a collegial, inside-industry tone [05:58]
• "We're way past memo here." – Michael Burgi on the exhaustive WPP documentation [13:30]
• "This is kind of just the cost of doing business." – Tim Peterson, on industry tolerance for principal media [06:04]
• "If that's a good friend, you probably give him one or two of those free beers that you got. And if you don't, maybe you question the friendship in the end." – Michael Burgi's analogy, poking fun at industry ethics [20:23]
• "When it comes to actual execution... not much." – Seb Joseph, on the lack of real change despite years of 'transparency' rhetoric [29:15]

Timeline of Important Segments

• 00:11 – Opening and set-up: Principal media’s persistent relevance
• 07:52 – What is principal media? Michael Burgi’s breakdown
• 11:04 – Why the issue is back: new lawsuits, contracts, and WPP scrutiny
• 14:08 – Internal WPP practices & document leaks (Richard Foster case, specifics of how rebates flow)
• 18:22 – Fundamental agency/client conflict & the case for/against principal buying
• 25:03 – Competitive implications: Holdco vs. independents
• 27:22 – Comparison to upfront TV & grocery store analogy
• 29:54 – Google/Meta as the new "principal buyers"
• 33:04 – The tax-preparer analogy: clients pay for expertise + risk, expect results
• 35:46 – Contracts and the limits of enforceable transparency

Conclusion

The episode underlines principal media's stubborn persistence and complexity in digital advertising. The practice is both a lifeline and landmine for agencies—a business necessity in squeezed-margin times, but also a breeding ground for opacity and skepticism among clients. Ultimately, the hosts and guests see principal media as neither all good nor all bad; transparency, contracts, and outcome-based measurement are the new battlegrounds, and the practice will likely stick around in ever more nuanced forms.

Final Thought:
"Outcome-based measurement, outcome-based buying—once that's really available and reliable, the rest of this just becomes noise." – Tim Peterson [34:00]