sellers.json and SupplyChain: the trust graph buyers underuse

sellers.json and SupplyChain: the trust graph buyers underuse

sellers.json (an SSP's public list of who it pays and is authorized to represent) and the SupplyChain object (the per-bid record of every intermediary that touched an impression) together form a verifiable graph of the supply chain. Most buyers check them for fraud only. They also encode cost.

Reading them as cost structure:
— Each node in the SupplyChain object is an intermediary taking a margin. A four-node chain to reach a publisher is, by construction, more expensive than a one-node direct path to the same publisher.
— sellers.json marks each seller as PUBLISHER, INTERMEDIARY, or BOTH. Long runs of INTERMEDIARY nodes signal resold-of-resold inventory with stacked fees.
— Comparing the same publisher's impressions across paths, the chain depth correlates with the gap between your price paid and the publisher's actual received revenue.

The action, step by step:
— Parse the SupplyChain object on incoming bid requests and tag each by node count and authorization status.
— Cross-check declared sellers against the publisher's own ads.txt and sellers.json to flag unauthorized or undeclared resale.
— Prefer the shortest authorized path to each publisher; throttle deep chains unless they uniquely deliver inventory you can't get direct.

Why it matters: the SupplyChain object isn't just a fraud signal — it's an itemized receipt of the intermediaries between your money and the publisher. Buyers who read it as a cost graph route around fee stacking that buyers who read it only for fraud never see.