Deduplicating bid requests cut self-competition that inflated CPMs 17%

Deduplicating bid requests cut self-competition that inflated CPMs 17%

A buyer found themselves repeatedly winning auctions against their own bids on the same impression, arriving through different SSPs.

1. From log-level data they keyed bid requests on a composite of user ID, placement, and a five-second time window.
— 19% of requests were duplicates: the same impression offered by two or more SSPs simultaneously.
2. On those duplicates, the DSP was bidding on each copy, so two of the buyer's own bids competed in a single downstream auction.
3. They enabled the DSP's deduplication, bidding once per unique impression at the cheapest available path.

Evidence: on the deduplicated segment, paid CPM fell 17% and win rate was unchanged, because the buyer stopped bidding against themselves and stopped paying a second-price set by their own duplicate bid.

Why it matters: when one impression reaches you through several SSPs, your own bids can become each other's competition, raising the clearing price you pay. Deduplicating on user-plus-placement-plus-time, then choosing the cheapest path, removes the self-inflicted floor.