<b>Duplicate bid requests: the same impression asks you twice</b>

<b>Duplicate bid requests: the same impression asks you twice</b>

In a header-bidding world, one ad slot can generate multiple bid requests that reach your DSP through different exchanges. You are being asked to bid on the same physical impression more than once, and how your DSP handles it changes your economics.

1. Identify duplication by hashing stable fields — user ID, slot/placement ID, timestamp window, page URL — across exchanges in your log-level data.
2. If your DSP bids independently on each copy, you can win the same impression's auction on two paths and effectively bid against yourself, or you win one and waste compute on the rest.
3. Worse, duplication inflates your apparent available supply and corrupts reach and frequency math, because two requests look like two opportunities when they're one.

The mitigation is request deduplication before bidding and choosing the single best path per impression — which is SPO operating at the request level, not just the seller level.

<b>Why it matters:</b> if your DSP doesn't dedupe, your supply path optimization is incomplete and your frequency capping is leaking, because the unit of analysis (a unique impression opportunity) is being double-counted upstream. Measure your duplication rate per publisher; double-digit percentages are common and quietly distort everything downstream.