In a second-price auction you never pay your own bid. You pay one cent more than whoever came second — which is what makes telling the truth about your price safe. Regulators say the runner-up was calculated by the house.
An advertiser sees a bill. To know it was too high, you would need the runner-up's bid — somebody else's private number, which you never see, and neither does your accountant or your agency.
And the price you should have paid is not hidden. It does not exist. It belongs to an auction that ran differently, so there is no file to demand and nothing to compare against. An advertiser who suspects something can lower their bid and watch what happens. That is not an investigation.
The mechanism surfaced the way anything unmeasurable surfaces: a prosecutor asked for the emails. According to the complaint filed on 31 August 2026, from 2019 an extra charge — internally a soft reserve — sat on top of the auction price. The executive running the advertising business wrote that the price advertisers pay "isn't set by an actual bidder" but is "a proxy second price that we calculate."
One measurement carries it: how often the winner ends up paying their own full bid instead of one cent above a rival. Three or four times in ten in 2021. Seven in 2022. Eight by 2024. The complaint says the charge was ramped gradually to avoid notice and pushed higher on the largest shopping days.
Amazon rejects the case. It says the average winning bid on these ads fell by half between 2019 and 2025; that advertisers saved more than $8bn from 2021 to 2025 as matching improved; that the inflation-adjusted price of a click did not move; and that no shopper anywhere is shown paying more. These are allegations, and a court has tested none of them.
Not the surcharge. Charging too much is legal. The statute in play forbids two things — misleading people, and treating them unfairly — and as the case is written, the weight sits on the first. The auction was described as second-price and allegedly worked otherwise. The centre of gravity is the label on the box, not the invented bidder inside it.
Which tells you what the rest of the rulebook contains. Neither half of that law says what an auction may do. One asks whether you were told the truth about it; the other asks whether the result was unfair, case by case, years afterwards, in front of a judge. There is no rule anywhere about how the machine may be built.
One half of the law asks whether you were told the truth. The other asks a judge, years later, whether the result was fair. Neither says what the machine may do.
A stock exchange cannot change a trading rule quietly. Under US securities law it files the change with the regulator and publishes it before it applies: the rule of the market is itself a public document. And the inside is recorded — after the 2010 flash crash, when prices fell and recovered within minutes and nobody could reconstruct why, the exchanges were made to build one shared record of every order, cancellation and trade. It takes in roughly 58 billion entries a day.
One country, two markets doing the same job. One is governed by its construction. The other is governed by its description. Which is what the alleged surcharge actually needed in order to work — not secrecy about the number, secrecy about the rule. On an exchange it would have arrived as a filed amendment, in public, before a dollar went through it.
The obvious fix is to change the auction: drop second price, make everyone pay their own bid, leave no gap. That was tried. In September 2019 Google moved its advertising exchange — the largest in the world — to exactly that, and announced it as a step toward transparency.
2019 is a busy year here. Google switched. According to the Seattle complaint, Amazon's surcharge began. And Google ended a separate programme of its own that prosecutors in another case say had been quietly reducing what website owners earned, in some cases by nearly half. Changing the format did not settle who sets the price. It moved where the question lives.
Paying your own bid has its own cost. If you pay whatever you write down, you learn to write down less than you mean — and doing that well is an algorithm trained on years of data. A format that looks fairer hands the advantage to whoever has the biggest machine. Among half a million small advertisers, that is nobody.
So the defect is not in the format. It is in the record — and the record has a bill. When the stock-market audit trail was approved, it was supposed to cost at most $55m a year; it passed $248m. In March 2026 the regulator approved cutting as much as $73m back out and reopened the whole design. One of its own commissioners calls it expensive, contentious and dangerous to privacy, because a single archive of what every investor ever did is also a single thing worth stealing. And a record prevents nothing. It only lets you look afterwards.
Europe built one. Its digital markets law requires the largest platforms to hand advertisers and publishers the measurement tools and the underlying data, free of charge, so customers can audit what they bought — what it cost, what the platform kept, how it performed. The European Commission's review of April 2026 reports that advertisers can now see things they could not see before.
Then ask who exercises a right like that. An audit is professional work at professional prices. For an advertiser spending a few thousand dollars a year — most of the half million small businesses in the case — the audit costs more than the overcharge possibly could. The right belongs to everyone and is used by the powerful, who were never the ones being quietly squeezed. And even a perfect audit meets the wall from the beginning: the data shows what you paid, never what you would have paid.
Which leaves the heaviest repair: stop whoever runs a market from also playing in it. That is what US prosecutors sought in the other big advertising case, and in April 2025 a federal judge agreed the law had been broken. By September 2026, seventeen months on, no remedy has been chosen. The judge has said she is unsure who could even buy the exchange, since the obvious buyers arrive with competition problems of their own, and that whatever she orders will be appealed for years. Every day of that argument, the auction runs under the old rules.
A record that costs a fortune and only looks backward. A right to audit that costs more than the theft. A separation slower than the harm it treats. And doing none of them is not free either — that price is the number in the complaint.
That is what made this possible, if the case is right. Not a clever trick — an absence. The rule of the auction lived in one place, inside the company running it, and no law required it to exist anywhere else first. Which is why the only repair that ends this case is a rewritten paragraph in the terms, after which the same machine runs on and everyone argues about whether that is now fair.
One more thing about the law being used. In 2021 the Supreme Court held, unanimously, that this regulator's main route to getting money back for the people it protects was never in the statute. So the money in the Seattle case rides largely on 22 states and their own laws, and nobody has named a figure.
Somebody set the price you just paid, using a rule. Where is that rule written — and did anyone outside the company have to see it before it was used on you?