The Digiday Podcast After WPP reckoning: The case for and against principal media
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Mar 17, 2026 Seb Joseph, Digiday executive editor who broke WPP document stories, and Michael Burgi, senior editor focused on media buying and agency practices, discuss principal media buying. They explain what principal deals are and why WPP revelations put the practice back in the spotlight. Conversations cover proprietary inventory, agency-as-supplier tensions, platform-driven principal products, and whether transparency can be a market advantage.
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What Principal Media Actually Is
- Principal media is agencies buying inventory themselves at discounted rates and reselling it to clients at a markup.
- Michael Burgi explains agencies reclassify rebates and proprietary inventory as revenue, hiding it in holding company reports.
Insist On Contract Clarity For Principal Deals
- Require contract clarity when onboarding agencies that use principal media, specifying how it's used and what transparency clients receive.
- Seb Joseph references Forrester guidance saying clients should ask what is bought and where ads run.
WPP Memo Shows Vast Unused Proprietary Inventory
- WPP internal documents from Richard Foster showed GroupM aggregated client budgets to hit volume thresholds and trigger rebates.
- Seb Joseph recounts that 97.4% of the proprietary inventory bought for top clients went unused, so clients didn't benefit.