Most paid media reporting is built around metrics the platforms choose. These are the ones we use instead, and why.
ROAS versus MER.
ROAS is revenue a platform claims for its own ads. MER is total revenue divided by total spend everywhere. When several channels run at once they all claim the same sales, so channel ROAS can look great while the business gets no better. MER is the one that can't be gamed.
TACoS.
Total advertising cost of sale: ad spend divided by total sales on a marketplace, including organic. Unlike ACoS, which counts only ad-attributed sales, TACoS shows whether your Amazon or Walmart advertising is lifting your whole listing or just buying sales you'd have made anyway.
Allowable acquisition cost.
The most you can pay to acquire a customer and still hit your margin and payback targets. It comes from your economics, not a platform benchmark, and it's what should set bid and budget ceilings rather than a round-number CPA goal.
Incrementality.
Whether an ad actually caused a sale that wouldn't have happened otherwise. Retargeting and branded search tend to look spectacular in platform reporting while producing little incremental revenue. Geo holdouts and spend tests are how you find out.
CTV versus OTT.
Connected TV means streaming content watched on a television through a smart TV or device. OTT is any content delivered over the internet rather than cable or broadcast, including phones and tablets. The practical difference is screen and attention: CTV behaves more like television, OTT more like digital video.
Frequency and saturation.
How often the same person sees your ad over a period. Past a certain point more spend stops reaching new people and starts annoying the ones you already reached, which shows up as rising costs with flat revenue. It's the most common reason scaling a campaign quietly stops working.