Myth: Block the cheap, low-quality domains and you'll spend better

Myth: Block the cheap, low-quality domains and you'll spend better

The clean-up instinct: pull a domain report, blocklist everything with suspiciously low CPMs and weird names, and assume you've upgraded average quality. Cheap looks like junk.

This conflates price with value and ignores how the bidstream labels inventory.

1. CPM is a clearing price, not a quality grade. A genuinely high-performing long-tail domain can clear cheaply simply because few buyers compete for it — that's an arbitrage, not a warning.

2. The names you'd blocklist are often declared domains via the publisher-passed domain field, which is forgeable. Domain spoofing means the junk you want to block may be masquerading as a premium domain you're keeping.

3. The proper hygiene layer isn't a CPM filter; it's ads.txt / sellers.json verification — confirming the seller is authorized to sell that domain — plus app-ads.txt for in-app. That catches spoofing a CPM blocklist never will.

4. Blocking by price also fights your own bid shading: cheap inventory that converts is exactly where shading earns its keep. You'd be cutting your highest-margin pockets.

The value question is performance-per-dollar by verified seller, not raw CPM.

Why it matters: a low-CPM blocklist optimizes against price and trusts a forgeable label. Real quality control runs on authorized-seller verification and post-bid performance, where cheap-but-real inventory is often your best buy.