The knowledge gap here is real. According to the ANA's 2024 report on principal media, only 48% of marketers said they were "very familiar" with the practice. That's less than half, despite the fact that usage has climbed to 58% of companies as of 2026.
This article covers what principal-based buying is, how it works, the benefits and risks it creates, and what marketers can do to protect themselves.
Key Takeaways
- Principal-based buying occurs when an agency purchases ad inventory at a discount and resells it to clients at a markup, without disclosing the margin.
- Unlike agent-based buying, the agency acts in its own financial interest, not solely the client's.
- Claimed savings range from 10% to 15%, yet 90% of marketers worry whether agency recommendations truly serve the brand.
- Protection starts with direct contract clauses, independent benchmarking, and fee-based partners whose incentives align with your outcomes.
What Is Principal-Based Media Buying?
The Core Definition
Principal-based buying occurs when a media agency stops acting as an "agent" for its client and becomes a "principal." It purchases ad inventory from publishers at a negotiated discount, then resells that inventory to its clients at a markup, without disclosing what it originally paid.
This stands in direct contrast to agent-based buying, where the agency negotiates on the client's behalf, passes through the actual media cost, and earns a transparent fee for the service. In the agent model, there is no hidden margin. The client knows what the media cost and what the agency earned.
A Brief History
The agency-as-intermediary model traces back to the 19th century. N.W. Ayer pioneered the "open contract" billing model in 1876, and a 15% commission on media billings became the dominant compensation structure for most of the following century. That commission structure gradually eroded, and with it came pressure on agencies to find other revenue sources.
The modern principal-based buying controversy came into sharp focus with the 2016 ANA/K2 Intelligence media transparency report, which found that non-transparent rebates and principal-transaction markups were widespread in the U.S. media ecosystem. Markups on media sold through principal transactions ranged from approximately 30% to 90%, none of it disclosed to clients.
The backlash prompted widespread contract reforms, but the practice didn't disappear. Today it's resurged as holding companies face compressed margins and seek alternative revenue streams, making it a live issue for any marketer reviewing agency contracts.
Principal vs. Barter: A Distinction Worth Making
Both involve agencies acting as principals, but they're not the same thing:
- Barter media involves remnant or last-minute inventory, often settled through non-cash compensation arrangements
- Principal media involves direct monetary transactions and frequently includes premium inventory commitments
The stakes are higher with principal transactions because the inventory quality and the undisclosed markup can be significant. The practice is most closely associated with large holding companies like Omnicom, Publicis, and IPG, but independent agencies are building their own versions as well.
How Principal-Based Buying Works in Practice
The Two Primary Mechanics
Principal-based buying takes two main forms:
- Direct inventory purchase: the agency buys specific ad placements from a publisher at a bulk discount, owns that inventory, and resells it to clients.
- Volume commitment deals: the agency commits to a certain level of spending over time in exchange for reduced rates from publishers, then fills that commitment through client buys.
In both cases, the agency controls the inventory and resells it. Forrester confirms that agencies use buying power to lock in rebates from publishers and media owners based on these upfront bulk commitments.
What the Client Sees (and Doesn't)
The client receives a media buy at a rate that's typically below standard publisher rate cards, and the savings are genuine. What's hidden is how much the agency paid, so the client cannot calculate the margin the agency earned on the transaction.
This is the core transparency issue that Digiday identified in its breakdown of the practice: the agency may not disclose what it paid for the inventory. The client sees a price, but not a margin. That's a meaningfully different information environment than agent-based buying.
In practice, this means two things:
- Visible: The placement rate, which appears competitive against standard publisher rate cards
- Hidden: The agency's actual cost and the markup built into the transaction
The Incentive Misalignment Problem
Because the agency has already committed to or purchased inventory, it bears financial risk if it can't move it to a client. Agencies commonly cite that risk as justification for the markup.
But owning inventory creates a direct conflict: the agency now has a financial reason to recommend that inventory regardless of whether it's the best fit for the client's audience. The ANA/K2 report found agencies faced documented pressure to direct client spend toward media companies where the agency or holding company held an economic interest, a structural dynamic that can quietly override what's actually best for the campaign.
The Benefits and Risks of Principal-Based Buying
Benefits for Marketers
The primary appeal is cost. ANA's 2024 principal media report states that principal media can produce media cost savings of 10% to 15%, and a case study in the same materials showed approximately 15% in savings that were reinvested into media research. In ANA's 2026 study, 76% of marketers cited reduced costs as the primary benefit.
Additional benefits include:
- Access to premium inventory that might otherwise be cost-prohibitive
- Budget predictability through locked-in pricing
- Protection from price spikes in scatter markets or auction-based programmatic environments
Those cost advantages are real, but they come directly from the same structural arrangement that introduces the model's biggest risks.
Risks Marketers Need to Understand
The risks are structural, not incidental.
Incentive misalignment. According to ANA's 2026 study, 90% of marketers expressed concern over whether principal-media recommendations are in the brand's best interest, up from 79% in 2024. That's not a fringe worry. It's the dominant concern among marketers who understand the model.
Transparency risk. Without disclosure of original costs or guaranteed audit rights, marketers have no way to independently verify whether they received the savings promised or whether media quality met their standards. The "black box" dynamic is what critics most object to, and governance is not keeping pace with adoption.
Media quality risk. Pre-purchased bulk inventory may not align with a brand's specific audience targeting needs. A deal optimized for volume and margin doesn't automatically deliver the precision or contextual relevance that performance-driven campaigns require.
Marketing Dive's coverage of the ANA's 2026 findings specifically identified loss of quality in media placement as a top advertiser concern.
Why Principal Media Is Growing
Principal media usage rose from 47% of companies in 2024 to 58% in 2026, with 56% expecting to continue using it in the coming year. That trajectory reflects real economic pressure on all three sides of the relationship.
Agency Margins Are Shrinking
Holding company margins are under sustained pressure. WPP reported a headline operating profit margin of 13.0% in 2025, down from 15.0% the prior year. Principal media offers a path to higher-margin revenue without adding headcount or overhead.
Omnicom reported $4.1 billion in third-party service costs in full-year 2025 (up 22.8%), a category that includes supplier costs when acting as principal, and a clear indicator of how much inventory agencies are committing to upfront.
CMO Budgets Are Flat
Gartner reports that marketing budgets flatlined at 7.7% of company revenue in 2025, and 59% of CMOs said their budget was insufficient to execute their strategy. With average CMO tenure at Fortune 500 companies sitting at just 4.2 years, the pressure to show visible cost efficiency is acute. Principal media offers a compelling pitch: lower CPMs, faster.
Publishers Want Predictable Revenue
Media companies benefit from committed agency volume in fragmented markets where scatter inventory can go unsold. Publishers actively provide rebates tied to upfront bulk buying, which is the supply-side incentive that makes the model financially viable for agencies in the first place.
According to the ANA's 2026 study, the practice is most common in television and the digital open web, the two channels where upfront bulk commitments have the longest history and the deepest publisher rebate structures.
How Marketers Can Protect Themselves
The ANA's 2026 guidance is direct: address principal media in agency agreements before transactions occur. Waiting until after a contract is signed leaves marketers with limited recourse.
Ask Your Agency Directly and Document the Answer
Before signing or renewing any agreement, ask whether the agency engages in principal-based buying, proprietary media trading, or purchase-risk inventory deals. Request a written answer documented in the contract. The question itself is clarifying.
Add Specific Contract Clauses
Key provisions to include:
- Audit rights over actual media costs
- Caps on spending within principal arrangements
- Full disclosure requirements on agency margin for any principal transaction
- Performance accountability tied to business outcomes, not just impression delivery
- Language explicitly prohibiting undisclosed markups or related-party benefits
Benchmark Independently
Use third-party media auditing services such as Ebiquity or FirmDecisions, or compare CPM rates against industry benchmarks to verify whether pricing is advantageous. Rate cards are not a neutral baseline. You need to understand what agencies actually pay, not what publishers list.
These three steps (direct questioning, contract protections, and independent benchmarking) give marketers concrete leverage before money moves.
Why Fee-Based Strategy-First Media Experts Offer a Different Model
The structural problem with principal-based buying is an incentive problem. When an agency profits from the spread between what it pays for inventory and what it charges the client, every recommendation exists in the shadow of that margin. You may never know which recommendations were purely strategic and which were partially motivated by inventory the agency needed to move.
A flat-fee model eliminates that ambiguity entirely. When an agency charges the same fee regardless of how much media is bought or which inventory is selected, there is no financial reason to favor one channel, publisher, or placement over another. Every recommendation is driven solely by what serves the client's audience and business goals, not by margin targets on the agency's side of the ledger.
Growth Marketing Werks operates on exactly this model. As founder and CEO Suzanne Corriell states directly: "Most agencies are just order takers, pushing generic campaigns with no strategy, no accountability, and fee structures that reward bloated media investment over real results. With flat-fee pricing and full-funnel expertise, our only incentive is your growth."
The team describes their approach as being "more like financial planners for your advertising dollars," and the comparison holds up. A fee-only financial planner has no incentive to recommend high-commission products. Neither does an agency whose compensation is entirely decoupled from media investment volume.
For marketers evaluating agencies, that decoupling is worth examining closely. It determines whose interests are actually being served when the media plan gets built.
Frequently Asked Questions
What is principal-based media buying?
Principal-based media buying is when an agency purchases ad inventory at a discounted rate and resells it to clients at a markup without disclosing its original cost. The agency shifts from acting as a client "agent" who passes through actual media costs, to acting as a "principal" that profits from the transaction margin.
What are the four main types of media buying?
The four primary types are:
- Programmatic buying: automated, auction-based, using DSPs
- Direct buying: negotiated directly with a publisher for specific placements
- Principal-based buying: agency purchases inventory and resells it to clients
- Agent-of-record buying: transparent, fee-based negotiation on the client's behalf
Most campaigns use a mix of programmatic, direct, and agent-of-record buying.
Is principal-based media buying legal?
Yes, the practice is legal in the United States. The core issue is not legality but transparency, specifically whether clients are fully informed about the arrangement and have consented to it through their contract. The ANA's position is that the risks are best managed through explicit contract language, audit rights, and disclosure requirements rather than through regulation.
How can I tell if my agency is using principal-based buying?
Ask directly in writing, and review your contract for language around "proprietary media," "purchase risk deals," or "third-party service costs." Check whether your agency discloses actual media costs or only presents a single bundled rate, and whether you have audit rights to verify either.
What contract clauses protect against undisclosed markups?
At minimum, your contract includes:
- Full disclosure of any principal arrangements
- Audit rights over actual media costs
- Spending caps on principal-based inventory
- Performance accountability tied to business outcomes
The ANA and Ebiquity/FirmDecisions published a recommended contract framework after the 2016 K2 report, a practical starting point for any negotiation.
How does principal-based buying differ from traditional agent-based buying?
In agent-based buying, the agency acts on behalf of the client, passes through actual media costs, and earns a transparent fee. In principal-based buying, the agency acts as the inventory owner and earns an undisclosed margin on resale, meaning the client has no visibility into what the agency actually paid.
