What is principal media?

So, what exactly is Principal Media?

Principal media, sometimes called inventory media, is where advertising agencies take a more direct role in media buying. Instead of acting purely as intermediaries for their clients, agencies purchase media inventory upfront from publishers. They then resell it to their clients, adding a markup.

It’s like a wholesaler with a velvet rope. Agencies claim ownership over the media inventory and become, in a way, their own media platforms.

In this model, agencies act not as agents working on behalf of their clients but as owners—or “principals”—of the inventory.

What this means for clients is a bit of a shift. On one hand, they’re accessing media inventory that the agency has already locked in, often at a discount. On the other, they’re stepping into a market where challenges like transparency, trust, and cost-effectiveness all come into play.

Why it's not just business as usual

Let’s lay out the stakes.

Bulk Purchases and Discounts: Agencies secure large volumes of media inventory at discounted rates, often through long-term commitments. This allows them to guarantee publishers steady revenue and, in theory, gives clients access to premium ad space.
Increased Profit Margins for Agencies: The agency isn’t just making money off traditional service fees—they’re earning additional revenue by reselling inventory they own.
Non-Disclosed Pricing: Agencies aren’t required to share the original cost of the media with clients, which gives them control over pricing.

While these elements might sound like a simple transaction shift, they introduce a new complexity in the client-agency relationship. Who’s benefiting most? And what’s the right way for clients to manage this setup?

Potential benefits for clients

Principal media does offer some possible upsides for clients, especially in terms of access to valuable ad space:

Preferred Access to Inventory: Agencies with large media portfolios can offer clients access to sought-after inventory that may not be as readily available on an open market.
Cost Savings: If managed well, clients could see cost savings on high-demand inventory that agencies secured at lower rates.

These advantages mean clients get stability in their ad placements—an attractive prospect for brands with high-volume advertising needs.

The transparency question

One of the main criticisms of principal media is transparency. When agencies resell inventory without revealing the original cost, it creates questions for clients:

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Is the agency giving the best deal, or simply marking up inventory for higher profits?

In fact, this lack of transparency has led to concerns about conflict of interest. If an agency has invested heavily in specific media, are they recommending it because it’s the best fit for the client—or simply because they need to sell it?

Real Talk: The Risks

For clients, the risks of principal media are significant:

Transparency Gone AWOL: Since agencies don’t disclose original prices, clients have no way of knowing if they’re getting gouged.
Brand Safety and Quality: Agencies might end up reselling inventory that isn’t exactly pristine. They have financial incentives to move what they own, not necessarily what’s best for the client.
Trust Issues: If clients can’t be sure they’re being treated fairly, it sours the whole relationship. When transparency falters, trust crumbles.

And let’s not forget the financial risk for agencies. They’re committing large sums to bulk media purchases, banking on a resale to clients. If they can't move the inventory, they’re stuck holding the bag.

Industry Perspectives: The Debate

The advertising industry is divided.

Supporters argue that principal media helps everyone involved. Agencies and publishers benefit from predictable revenue, while clients can access premium inventory that might otherwise be tough to secure.

Critics, on the other hand, worry that this model blurs the lines of trust. If an agency acts as both buyer and seller, who are they really prioritizing? While some clients appreciate the access, others find themselves questioning the authenticity of agency recommendations.

Numbers to Know: Prevalence and Growth

A May 2024 report by the Association of National Advertisers (ANA) shows this practice is more than a passing trend:

41% of marketers expect to adopt principal media in the coming year.
24% of current users are planning to ramp up usage.

The numbers suggest that principal media isn’t going anywhere. If anything, it’s set to become more mainstream, raising questions about the future of client-agency relationships.

An examination of WPP's financial reports and earnings calls reveals that media purchased for resale to clients represented 32% of GroupM’s $8.7 billion revenue last year.

Across the major holding companies—the "Big Four"—these pass-through costs, primarily from media bought and resold to clients, totaled roughly $11 billion out of $60 billion in combined gross revenue, according to Brian Wieser, principal at Madison and Wall consultancy.

Notably, WPP is the only holding company that provides a distinct breakdown of media pass-through costs, detailing what it spends to purchase media for resale. This transparency allows for more precise analysis.

Tips for brands

If your agency offers principal media options, here are some steps to ensure you’re maximizing the benefits while minimizing risks:

Train Your Team: The more your team understands the principal vs. agent model, the better. You are spending millions. Get educated.
Set Clear Contract Terms: Make sure your agreements with agencies include transparency clauses. These should outline whether your agency is acting as an agent or principal and include details on pricing and quality standards.
Insist on Audit Rights: Audits are key. By having a clear process for auditing media purchases, you’ll have more confidence that your agency is delivering value.
Evaluate Inventory Quality: Understand the kinds of inventory you’re buying. High-quality, brand-safe placements are a must, so ask questions if details seem vague.
Consider Brand Safety: Brand safety should be non-negotiable, and contracts should reflect this. You want reassurance that your ad placements align with your brand’s standards.
Foster Open Communication: Keep a strong dialogue with your agency about their practices, and make sure they understand your expectations regarding transparency and quality. This is not a one-time discussion. You are going to feel like a broken record, but that is required.

What’s next?

The use of principal media is likely to keep growing, but so is scrutiny (lord willing). Industry watchdogs and clients alike are starting to push for more transparency, which should lead to new norms and regulations. A lot more attention is needed.

For now, clients must rely on their own strategies to protect their interests and make sure they’re getting real value from these partnerships.