A decade after the Association of National Advertisers (ANA)’s landmark K2 report exposed systemic corruption in media buying, fresh survey data shows advertiser concerns about agency transparency have barely budged since 2014 — and are heading in the wrong direction.“I feel a bit like a broken record,” attorney Keri Bruce said near the end of a virtual ANA session marking the report’s anniversary. “But that’s okay,” ANA group EVP Bill Duggan replied, “because we’ve said this now for 10 years, and some people still don’t get it.”Fielded in May among 108 ANA client-side marketers, the new data released June 1 showed that 43% of advertisers still have concerns about the level of transparency with their media agencies. In a comparable ANA and Forrester survey from 2014, that number was 46%. The needle has hardly moved. Worse still: Among those with concerns today, 49% say their concerns have increased over the past year, up from 42% in 2014, with principal media — where agencies buy media inventory in bulk and resell it to clients — as the most frequently cited reason. “Not real progress here, unfortunately,” Duggan said.The original key players behind the K2 report gathered to take stock — and found little to celebrate.The original reckoningWhile concerns about agency rebates were already surfacing in ANA committee meetings as early as 2010, former Mediacom CEO Jon Mandel lit the fuse. His blunt speech at the ANA Media Conference in March 2015 — where he used the word “kickbacks” — set off a firestorm. Several months later, the ANA hired investigative firm K2 Intelligence to separate fact from fiction. The report confirmed what many had suspected but few had said publicly: non-transparent business practices — hidden rebates, undisclosed markups, media inventory purchased for one price and sold to clients for another — were not isolated incidents but systemic features of the media agency model. Richard Plansky, who led the K2 investigation and is now at financial and risk advisory firm Kroll, recalled what most surprised him: “a fundamental disconnect in the understanding of the basic nature of the advertiser-agency relationship.” Advertisers assumed their agencies operated as fiduciaries — entities legally and ethically bound to act in their clients’ best interest. Agencies, for the most part, acted differently: The relationship was defined by the contract, not by any assumed loyalty. “You have one party that thinks, ‘Well, we’re married,’” Plansky said, “and the other party is like, ‘We’re not even dating.’”K2 found these problematic practices happening on myriad media channels across holding companies and independents with what Plansky described as “high-level buy-in” from senior executives. These practices, he added, “rather than being bugs, were actually features. They were woven into the culture of these businesses.”A decade of whack-a-moleThe survey also showed that 56% of advertisers have updated their media agency contract within the past year — a number Duggan called “pleasantly surprising.” But that optimism was complicated sharply by what those updates did and didn’t cover: Only 54% have addressed rebates in their contracts, and just 61% principal media. Roughly a quarter didn’t know whether their contracts covered either issue.“How is it even possible that a company has a media agency contract that does not address rebates?” Duggan asked. Bruce, a partner at law firm Reed Smith (ANA’s outside legal council) who contributed to the ANA’s media agency contract template — now over 80 pages and updated three times since 2016 — said the deeper problem isn’t the contracts themselves. “What I don’t see enough of is operationalizing. You spend a lot of time, energy and effort putting contracts in place, but you need to comply with them on both sides.”Meanwhile, the landscape around those contracts has grown more complex. Walled gardens, CTV, retail media networks and the programmatic supply chain have added new layers of opacity since 2016. The intermediary chains have grown longer. The arbitrage opportunities have multiplied. And now, holding companies whose traditional revenue streams in creative and PR have eroded are leaning harder into principal and proprietary media as a margin lifeline, said Nick Manning, a former senior member of the Ebiquity/FirmDecisions team that released a follow-up framework one month after the K2 report was published.Manning offered an observation that cut against easy villain narratives: The day-to-day agency contact, he said, is effectively caught between two bosses — the client in front of them and the agency leaders above. “It’s very difficult to serve two masters equally,” he said.The underlying economics, Manning explained, had been rife in Europe and Asia-Pacific long before taking hold in the U.S. Agencies learned they could set artificially low headline fee rates, the visible upfront fees charged to clients, “because they knew they could make money through other non-transparent means behind the scenes.” That drove headline rates lower, while the mechanism for back-end revenue shifted: “from cash rebates to things like principal media. It’s a bit of a chasing game — or whack-a-mole.” The WPP case and what it revealsTen years on, the evidence isn’t only in the archives. Manning described the ongoing case of Richard Foster, a senior WPP executive suing the company for wrongful dismissal after allegedly raising concerns internally about GroupM’s principal media practices.According to Foster's filings, WPP booked approximately $1 billion in net sales from principal media in 2024 — roughly half the company’s entire profit for that year. Foster allegedly raised concerns about whether rebates that should have been returned to clients were being retained. WPP has disputed the characterization.The case also illuminated the gap between the industry’s public narrative about principal media adoption and what clients are actually agreeing to: Large numbers of WPP clients actively declined to opt into principal media programs yet still contributed to the volume negotiations that made those programs profitable for others, Manning said. He added that those who opted out, in effect, subsidized those who opted in.Despite the volume of industry conversation around principal media, Manning said it still accounts for just 10% of the U.S. market — citing the ANA’s latest principal media report — a figure that may surprise given how loudly the holding groups have been beating the drum. The push is coming from the agencies, not advertisers, and they’re finding themselves “pushing water uphill.”What comes nextIf the original K2 report was about rebates, the 2026 version of the problem is programmatic — and beyond that, agentic AI-powered media trading. Critics have long argued that programmatic was supposed to bring efficiency and accountability to media buying; instead, in Mandel’s words, it became “the first step to the black box — into the deep, deep black box.”Now, Manning warned, the big holding groups are building agentic media trading systems for reasons of arbitrage. “If anything, it’s going to make it a lot worse.” Mandel’s prescription: Don’t use your agency’s AI to prove your agency’s work — use your own, or an independent auditor’s. “There’s that old cliché: trust but verify. I would say it’s more: verify, verify, verify, and then maybe do a little bit of trust.”Any advertiser spending $50 million or more on media needs a dedicated internal head of media, Duggan said. The job has become too complex and too fragmented for a CMO to handle alongside everything else.The stakes are too high to treat media as anything less than a core business investment, said Mandel, who is now chairman and CEO of marketing and media consultancy Dogsled Enterprises: “Bad media can kill and bury great creative, but great media can save mediocre creative. If you want your business to grow, treat it as such.”Ten years. Same conversation. The record keeps skipping.