It&#x27;s not that simple. At any one time, a publisher can be serving ads from a few exchanges, a few different private sellers, and custom built ads for brands. And these all are served in different combinations across several different ad units on multiple pages. And some of those ad sellers may be backfilling with other ad networks, or maybe the publisher is backfilling certain ads from the ad exchanges at certain CPM prices.<p>I&#x27;d liken it more to a hardware product being shipped with faulty materials when multiple manufacturers are involved and it&#x27;s extremely difficult to identify the responsible party. Sure, they&#x27;re responsible for the end product, but it&#x27;s not so black and white.