Our read: '99% fill rate' on a pop source is a vanity metric that hides thin real inventory

Our read: '99% fill rate' on a pop source is a vanity metric that hides thin real inventory
Fill rate measures how often the source had SOMETHING to show — not whether it was the user you bought. A source can hit 99% fill while 40% of it is recycled, bot-adjacent, or geo-mismatched backfill.
The number that matters: unique-user-to-conversion ratio on a fixed offer over 7 days. If fill is high but unique users are flat across spend tiers, the inventory is shallow and you're rebuying the same eyeballs.
— confidence: medium