<b>My ROI dropped 20 points and I hadn't touched a thing</b>
No creative change, no offer change, no targeting change. The auction moved under me.
<i>The setup</i>
— Stable evergreen campaign, $16 payout, ~$1,500/day, ROI 38% for a month.
— Then it slid to 18% over ten days for no reason I could see in my account.
<i>The move</i>
I almost rebuilt everything. First I checked CPMs against my own historical baseline.
<i>The numbers (illustrative)</i>
— Average CPM rose 31% in those ten days, a big advertiser had entered my niche/GEO and bid up the auction.
— My conversion rate was flat. My cost side simply inflated.
— Same machine, thinner margin, entirely external.
<i>The lesson</i>
Margin compression often comes from outside your account. When ROI slides with no internal change, suspect the auction before you suspect your funnel. You can A/B test creatives forever and never beat a bidding war you didn't know you were in.
<i>What I'd do differently</i>
Track CPM as a first-class metric, not an afterthought. Diversify across 2-3 traffic sources so one source's CPM spike can't sink the whole operation. Concentration feels efficient right up until the auction turns.
Arb Files
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