Principal media buying has moved from a niche agency practice to a mainstream one, and most marketers are still governing it with contracts written for a different model. In a principal arrangement, the agency is no longer simply your agent placing media on your behalf at cost plus a fee. It buys inventory for its own account, often in bulk, and resells it to you at a price it sets. That can lower your costs. It can also blur whose interests the media plan serves. This guide explains how principal media buying works, why it is growing, where the risks sit for luxury and high-consideration brands, and the specific questions to put to any agency before you sign.
What Is Principal Media Buying?
Principal media buying is any arrangement in which the agency, or a company it owns, takes title to media inventory and resells it to the advertiser rather than buying it as the advertiser's disclosed agent. The industry uses several names for the same idea: principal-based buying, proprietary media, inventory media, and outcome-based media. The UK advertiser association ISBA, in guidance covered by Marketing Week in February 2026, describes it as agencies buying inventory, often in bulk, and reselling it to clients at a markup, frequently without disclosing what they paid or how much they added.
Three features define it:
- The agency is the counterparty. You buy from the agency, not through it.
- The price is a resale price. You see what you pay; you usually do not see what the agency paid.
- The agency carries some risk. It may have committed to volume in advance and needs to sell that inventory on.
None of that is inherently improper. Brokers, wholesalers and resellers operate this way in every industry. The issue is that a media agency is also the adviser recommending which media you should buy, and principal inventory gives it a commercial interest in that recommendation.
How Does Principal Media Buying Differ From Agency-Model Buying?
| Dimension | Agency (disclosed) model | Principal media buying |
|---|---|---|
| Who holds the media contract | Advertiser, with the agency as agent | Agency or its trading arm |
| Price visibility | Net media cost disclosed; agency fee separate | Resale price only; underlying cost usually undisclosed |
| How the agency earns | Fee or commission agreed in the contract | Margin between purchase and resale price, sometimes plus a fee |
| Audit rights | Typically full rights to invoices and supplier contracts | Often limited to what the agency invoiced you |
| Neutrality of recommendations | Agency is paid regardless of which media is chosen | Agency earns more when principal inventory is chosen |
| Placement and log-level data | Generally available on request | Varies; sometimes aggregated or withheld |
| Cancellation terms | Follow the publisher's terms | Follow the agency's terms, which may be stricter |
| Typical channels | All | Linear TV, CTV packages, open-web programmatic, print, radio |
The practical difference is the conflict of interest. In the disclosed model, your agency's income does not depend on which publisher wins the plan. Under principal media buying, it can.
Why Is Principal Media Buying Growing So Quickly?
The Association of National Advertisers published a study in March 2026, The Continued Acceleration of Principal Media, based on a survey of 114 client-side marketers. Its headline findings:
- 58% of marketers said their companies had used principal media in the past year, up from 47% in the prior study.
- 56% expected to use it in the coming year, up from 41%.
- 90% said their top concern was uncertainty about whether recommended principal media serves their best interest, up from 79% in 2024.
- Only 57% said their company had guidelines governing principal media, and 63% said their agency contracts addressed it.
- 76% cited reduced costs as the main benefit, and usage was highest in television (74%) and the digital open web (43%).
The drivers are not hard to see. Advertisers have pushed agency fees down for a decade, and principal trading is one of the few profit pools left to agencies, a point ISBA's own guidance acknowledges. At the same time, programmatic and CTV make it easy to package inventory, data and technology into a single bundled price that is difficult to compare.
Are There Real Benefits to Principal Media Buying?
Yes, and a balanced evaluation should acknowledge them. Agencies that commit volume in advance can secure lower unit prices than a single advertiser could. Principal deals sometimes include guaranteed delivery, make-goods or outcome guarantees that a disclosed buy would not. Some packages give access to inventory or data that is otherwise hard to reach, particularly in linear TV and large CTV publisher bundles.
The question is never "is principal media good or bad." It is whether a specific principal placement, at a specific price, is the best option for your objectives, and whether you have enough information to judge that.
What Are the Risks for Luxury and High-Consideration Brands?
For brands selling products above $5,000 to affluent audiences, principal media buying carries some specific risks beyond general transparency concerns.
- Inventory fit. Bulk-purchased inventory is bought to resell across many clients. It is optimized for broad reach at low cost, which rarely matches the narrow, premium audience a luxury brand needs.
- Supply quality. Open-web principal packages can include long-tail and made-for-advertising sites that drag down brand safety and attention.
- Hidden effective CPMs. A package that looks inexpensive at the bundled CPM may cost more per qualified household reached once you account for waste.
- Lost data. Without placement-level and log-level reporting, you cannot see where your ads ran, which makes optimization and incrementality testing harder.
- Contract lock-in. Prepaid or committed principal inventory can be difficult to cancel when results disappoint.
These risks compound in high-consideration categories because the audience is small. When only a few hundred thousand households can buy your product, every impression placed outside that group is pure cost.
What Should Brands Ask Agencies About Principal Media Buying?
Ask these questions in writing during any agency review, and ask them again at contract renewal. They apply to every agency, including holding company shops, independents and specialists. We would expect any agency on your shortlist, Stillwater Media included, to answer every one of them on paper.
Questions About the Agency's Role
- Does your agency, or any company in your group, buy media as principal? Ask for a yes or no, then a list of the trading entities involved.
- Which line items in our proposed plan are principal inventory? Every principal placement should be flagged in the plan itself, not disclosed in a footnote.
- What percentage of our total spend would be principal media? Ask for the figure by channel.
- Will you commit to recommending principal inventory only with our prior written approval? Consent should be specific to each buy, not blanket.
Questions About Pricing and Margin
- What margin or markup do you earn on principal inventory? Some agencies will disclose a range; some will not. The answer, or the refusal, tells you something.
- How does the principal price compare with a disclosed buy of equivalent inventory? Ask for a side-by-side.
- Are any rebates, volume bonuses or incentives received from media owners on our spend? Ask whether they are passed back to you.
- Are technology, data and media fees bundled? Request each cost separately.
Questions About Data, Audit and Exit
- Will we receive placement-level and log-level data for principal buys? Without it you cannot verify delivery. Our guide to log-level data in programmatic explains what to request.
- What audit rights do we have over principal transactions? Ask specifically whether auditors can see the agency's purchase cost.
- What are the cancellation terms for principal inventory? Compare them with your standard media cancellation terms.
- Who owns the data generated by our campaigns? That includes audience segments built from your exposure data.
An agency that answers these questions clearly and quickly is usually one you can trust with principal arrangements, if you choose to allow them. An agency that answers vaguely is giving you the most useful information of the whole review.
What Should Your Agency Contract Say About Principal Media?
At a minimum, the agreement should cover:
- A definition of principal media broad enough to include proprietary, inventory and outcome-based arrangements and any affiliated trading entity.
- Opt-in consent: no principal media without written, transaction-specific approval.
- Clear labeling of principal line items in every plan, invoice and report.
- Spend limits, such as a ceiling on principal media as a percentage of total spend.
- Data rights: placement-level reporting and log-level access on request.
- Audit rights that extend to principal transactions and affiliated entities.
- Rebate disclosure and pass-back terms.
- Exclusion from pitch guarantees, so an agency cannot meet a savings promise by moving you into principal inventory.
ISBA's guidance also recommends aligning finance, procurement, marketing and media teams internally on whether principal media is acceptable at all. That conversation is worth having before you start an agency review.
How Can You Tell If Principal Media Is Already in Your Plan?
Common warning signs include:
- CPMs that look meaningfully cheaper than market rates for apparently similar inventory.
- Plan lines described as "packages," "bundles," "trading deals" or "guaranteed outcomes" without a named publisher.
- Reports that aggregate delivery by category rather than by site, app or channel.
- Reluctance to provide supplier invoices or log-level files.
- Invoices from a trading entity whose name differs from your agency's.
How Do Disclosed Costs Compare?
The best defense against hidden margin is knowing what transparent buying costs. For managed programmatic and CTV on premium supply, these are Stillwater planning ranges rather than industry surveys:
| Cost layer | Transparent range (Stillwater planning range) | What to watch for |
|---|---|---|
| Agency management fee | 10% to 20% of media | Fees far below this often signal margin elsewhere |
| DSP platform fee | 10% to 20% of media | Should appear as its own line |
| Third-party data | $0.50 to $3.00 CPM | Bundled data makes waste invisible |
| Verification and measurement | $0.05 to $0.25 CPM | Should be named by vendor |
| Supply path fees (SSP and exchange) | 10% to 20% of working media | Reducible through supply path optimization |
If an agency's total cost looks far below the sum of these layers, ask how it makes money. The answer may be principal inventory. Our programmatic fee transparency audit guide walks through how to reconcile the layers line by line.
Common Mistakes Brands Make With Principal Media Buying
- Banning it without asking. An outright prohibition can remove legitimate options. Consent and disclosure usually serve brands better than a blanket ban.
- Allowing it without consent. The opposite error, and the more common one: contracts that are silent on principal media effectively permit it.
- Comparing headline CPMs. A cheaper CPM on lower-quality supply is not a saving for a brand with a narrow audience.
- Accepting aggregated reports. If you cannot see where ads ran, you cannot evaluate the buy.
- Letting pitch savings drive the decision. Savings promises in an agency review are easiest to meet through principal trading.
- Leaving procurement and marketing misaligned. Procurement may push for lower costs that only principal media can deliver, while marketing bears the quality risk.
Choosing a Model That Fits a Luxury Brand
For most high-consideration brands, the safest structure is a disclosed agency model with principal media permitted only on an opt-in basis, clearly labeled and capped, alongside private marketplace deals bought directly with premium publishers. If you are weighing whether to keep buying in-house or bring in a partner, our comparison of in-house programmatic versus an agency covers the governance trade-offs.
Work With an Agency That Answers in Writing
Stillwater Media is a selective performance media agency for luxury and high-consideration brands. We plan premium CTV through private marketplace deals, affluent audience engineering, programmatic, DOOH and streaming audio, with incrementality testing built into every plan, and we take on a limited number of engagements each quarter.
If you are reviewing agencies and want clear answers on how your media is bought, apply to work with Stillwater Media.
About the author: Stillwater Media is a selective performance media agency for luxury and high-consideration brands, headquartered in Charlotte, NC and working with clients nationally and internationally. The team plans premium CTV, programmatic, affluent audience targeting, DOOH, streaming audio, YouTube Select, podcasts, native and social for brands where customer lifetime value exceeds $5,000 and sales cycles run longer than 30 days, including private aviation, luxury real estate, wealth management, private clubs, luxury automotive, premium DTC and luxury hospitality. Signal. Strategy. Scale.
Frequently Asked Questions
What is principal media buying?
Principal media buying is when an agency, or a company it owns, buys media inventory for its own account and resells it to the advertiser at a price it sets, rather than buying as the advertiser's disclosed agent. It is also called principal-based, proprietary, inventory or outcome-based media, and the agency's markup is usually not disclosed.
How common is principal media buying in 2026?
In the ANA's March 2026 study of 114 client-side marketers, 58% said their companies had used principal media in the past year, up from 47%, and 56% expected to use it in the coming year. Usage was highest in television at 74% and the digital open web at 43%.
Is principal media buying bad for advertisers?
Not necessarily. It can lower prices and include guarantees, but it creates a conflict of interest because the agency earns more when its own inventory is chosen, and it often limits price visibility and audit rights. The safest approach is opt-in consent, clear labeling and a spend cap in the contract.
What should I ask my agency about principal media?
Ask whether the agency or any affiliate buys as principal, which plan lines are principal inventory, what share of spend that represents, what margin it earns, whether rebates are passed back, and whether you get placement-level data and audit rights over those transactions. Ask for the answers in writing.
What should a media agency contract say about principal media?
It should define principal media broadly, require written approval for each principal buy, label principal line items in plans and invoices, cap principal spend, guarantee placement-level and log-level data, extend audit rights to affiliated trading entities and exclude principal media from pitch savings guarantees.
