It has become clear recently that some sellers in the RTB ecosystem are engaging in abnormal practices regarding how IDs are populated in bid requests.
These sellers are causing a cookie ID to be presented in the bid request, in the customary field (“buyeruid”), but this cookie is not present in the browser. MediaMath listed this manipulation of IDs as unacceptable in its 2018 open letter to suppliers – yet it’s still occurring in 2024 at a concerning rate.
Typically, this misrepresentation is due to the practice of “ID bridging.” Sellers sometimes present a cookie ID through probabilistic bridging they claim is from another device that someone in a household owns. They do so to increase the monetization of their cookieless inventory, because without an ID, the inventory will attract fewer bids at lower prices.
The problem is not ID bridging, which is conceptually similar to cross-device targeting as provided by most DSPs. Buyers are objecting to unexpected, undisclosed manipulation of critical data in bid requests by sellers, without regard to negative side effects for the buy side.
Cookie syncing vs. ID bridging
The “buyeruid” field in bid requests is where an exchange is expected to put a DSP’s cookie-based user ID resulting from a customary cookie sync. This has been well-established behavior for as long as OpenRTB has existed. Deviating from this – such as presenting a “related” bridged ID – is surprising and unexpected from a buy-side perspective.
Though some sellers and tech vendors claim ID bridging is only being done with express permission from the DSPs, it often occurs without DSPs’ knowledge.
The integrity of IDs in bid requests is paramount. The accuracy of IDs is critical to ensuring audience targeted campaigns are bidding on the correct people, frequency capping occurs as expected and conversion attribution and other measurement can occur successfully. When a user does not have a cookie or the browser does not allow third-party cookies, the correct ID to present in “buyeruid” is none at all.
Buy-side concerns
The negative side effects of this practice include serving ads to a different person than intended, inhibiting frequency capping and lowering conversion rates (because conversion attribution cannot successfully occur for the impressions purchased).
ID manipulation also interferes with the accuracy of reach and frequency metrics and of DSP-provided cross-device targeting.
Even if the negative side effects were mitigated, ID bridging has significant potential to be abused for fraudulent purposes by sellers presenting IDs that are more likely to be bid on, rather than attempting to perform the practice accurately.
There is no reasonable way for the buy side to assess the accuracy of bridged IDs listed in bid requests. History has indicated that bad actors will blatantly lie about signals for financial gain.
Blocking bridging
Regardless of Google’s cookie course correction, far fewer users will have cookies enabled in the future, presenting challenges for every company in our ecosystem. However, unilaterally deployed, deceptive practices should not be acceptable. DSPs can compare the cookie IDs they see in bid requests to those they directly observe when serving the impression, to identify and block supply where discrepancies are occurring.
But cookie bridging isn’t the only area where these mismatches are happening. The same concerns apply for the “ifa” field used for declaring mobile or CTV advertising IDs. Unlike “buyeruid,” there isn’t a viable buy-side method for validating accuracy or determining how frequently bridging or other substitutions are occurring. However, it’s fair to assume that those who are manipulating “buyeruid” are doing similar for “ifa” as well.
The industry stance should be simple: In the absence of express negotiation between parties to the contrary, customary behavior should be expected for labeling IDs in the “buyeruid” and “ifa” fields.
The “buyeruid” field must only be used to provide a cookie ID resulting from a conventional cookie sync. The “ifa” field must only be used to provide a mobile or CTV advertising ID as retrieved directly from the device.
If a seller wishes to provide a bridged ID, they must do it in a clear, transparent manner, separate from these traditional fields. The IAB Tech Lab specs under development will provide a method for doing so. Buyers should have no objection to the presence of bridged IDs in bid requests if they are clearly disclosed and put in the appropriate place.
Clearer disclosures, as provided for in the proposed specs, would ensure that whether such an ID is used and for what purposes is under buy-side control. This way, outright fraud and the negative side effects that result from ID discrepancies can be avoided.
“Data-Driven Thinking” is written by members of the media community and contains fresh ideas on the digital revolution in media.
Follow Basis Technologies and AdExchanger on LinkedIn.
For more articles featuring Ian Trider, click here.
