Transaction IDs (TIDs) have been the topic du jour on LinkedIn and Twitter – and for good reason. These OpenRTB identifiers let buyers deduplicate the cluttered bidstream.
The entire TID debate has a clear subtitle: “Duplication is waste.”
However, legitimate auction duplication provides benefits for publishers. And the use of TIDs drives publishers’ fears around data leakage and buy-side power aggregation.
While TIDs have been around for a while, the recent kerfuffle kicked off with a LinkedIn post from The Trade Desk exec and Sincera co-founder Mike O’Sullivan. This sparked a productive conversation about the trade-offs between buy-side transparency and sell-side data control.
The drama escalated when Prebid (the main technology used by all web publishers to control their ad auction) announced changes to TIDs designed to protect publisher data and make them less useful for buy-side deduplication.
All of this maneuvering on TIDs misses a separate market failure: bidding rings.
What a bidding ring looks like in programmatic
Classical auction theory defines a bidding ring as a group of bidders who pre-coordinate, choose a representative and suppress the number of bids that reach the main auction. Imagine a fine art auction with 30 potential buyers. If 25 of those buyers discussed a strategy beforehand and only one of them showed up to the auction, that’s a bidding ring.
Programmatic’s version is not a conspiracy, but rather a function of how the industry has evolved. DSPs run internal meta-auctions across many advertisers and strategies, then shade and emit a single best bid to the exchange or publisher.
The effect on the sell-side auction is the same as a bidding ring: lower external bid density, muted demand signals and thinner price discovery. Visibility into bidding competition within the publisher’s auction collapses. Prices are pushed down not because demand vanished, but because it’s been aggregated and obscured.
A healthy market requires both buyers and sellers to have strong access to information. Bidding rings stifle that for sellers.
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Why duplication helps
Given this reality, some supply duplication isn’t a scam; it’s a counterweight that restores competitive pressure and price discovery on the sell side.
For publishers, auctioning the same impression through multiple exchange partners isn’t wasteful duplication; it’s smart multi-auctioning. Multi-auctions rebuild bid density, which increases the number of distinct opportunities for hidden valuations to surface.
Here are four reasons duplication matters to publishers:
1. Conducting multiple auctions aids in price discovery. With more paths, publishers get more independent samples of buyers’ willingness to pay. That sharpens floor setting and reduces the “guesswork premium” publishers otherwise must add.
2. Multi-auctions counter information asymmetry. When buyers see everything (via logs, identity, path data) and sellers see only one external bid, the market tilts. Multi-auction shifts some power back by forcing more bids to the surface.
3. Pipes fail, pacing changes and brand safety lists get updated. Having diverse bidding paths reduces the risk that one decision upstream is silently blocking demand.
4. Multi-auctions spread revenue across multiple supply platforms, and competition among supply-side platforms ensures they are always iterating, working to help publishers and advertisers. A major reduction in the landscape of supply partners would cause stagnation. Innovation and competition are invaluable.
Healthy vs. harmful multi-auctions
However, not all duplication is equal. Healthy auction duplication patterns share four traits:
1. Clear labeling: Every path cleanly identifies the seller, publisher and placement. No mislabeling to “game” uniqueness.
2. Core metadata overlap: Buyers shouldn’t see different user IDs or other core metadata across multi-auctioned bid requests.
3. Meaningful variation: Paths should differ in ways that matter—deals, data or packaging—not random reselling.
4. Frequency capping guards: Buyers need to have algorithms in place to ensure that multi-auctions don’t cause issues with their frequency capping systems.
Harmful duplication, by contrast, is noisy reselling that adds no signal, confuses attribution or is designed to mask provenance.
Another controversial topic is setting different floor prices per path, but this is a critical tool in the publishers’ toolbox to give better insight into the value of impressions. Multi-floors provide a sell-side counterweight to bid-shading algorithms on the buy side. There’s no backup in auction theory to support the statement that a single impression should only have one floor regardless of path.
Why not just fix the ring?
The cleaner long-term fix would be to let more bids out of the ring. At least two key things need to happen to make this a reality.
The first is multi-bidding. DSPs would need to update their logic to emit multiple ranked bids for the same opportunity. This preserves buyer efficiency while restoring sell-side density and exposing the demand curve (#1 vs. #2, #3, #4 deltas). It also reduces the need for heavy duplication upstream. And multi-bids need to be submitted from the SSP to the publisher.
The second fix is awareness of legitimate duplication, rather than punishing supply paths where duplication occurs. Sellers have legitimate concerns that TIDs will be used to deduplicate everything without regard to the impact on the seller. This is path punishment. Buyers should be aware of identical requests but avoid blanket penalties that erase legitimate path diversity. TIDs are a great solution here, but alone they could lead to a further collapse of publishers’ bid density.
The bottom line
Transaction IDs can benefit the ecosystem, but not if they result in information asymmetry.
Solutions need to be found that reduce bad duplication but do not reduce bid density. If DSPs are getting access to significant new information, publishers should get access to the same.
Bidding rings suppress visible competition in publisher auctions. Done transparently and with guardrails, multi-auctions counter the structural dampening of demand, restore price discovery and keep the open internet from behaving like a single-buyer market.
In today’s programmatic world, treating all duplication as bad is wrong; it can serve a critical role in ensuring a fair, competitive and robust marketplace.
“The Sell Sider” is a column written by the sell side of the digital media community.
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