The problem is not the overcounting itself. The problem is what you do because of it.
If Meta is reporting a 4.8× ROAS and you believe it, you put more money into Meta. If Google is reporting strong performance and you believe it, you protect that budget. If your email platform is showing high revenue attribution, you feel confident about the channel mix.
Meanwhile your blended CAC is quietly climbing. Your true profit per order is falling. And you have no reliable way to know which channel is actually driving incremental revenue versus which one is just claiming credit for sales that would have happened anyway.
Reported ROAS vs true ROAS — the typical gap
True ROAS is calculated after removing duplicate attribution, subtracting COGS, returns, fulfilment costs and Shopify fees. The reported number looks healthy. The true number tells a different story.
The brands that discover this discrepancy tend to find one of two things. One channel is dramatically more efficient than the dashboards suggest — usually email, or a specific retargeting audience, or a specific market — and it is being underinvested because the signal is obscured. Or one channel is significantly less efficient than it looks, and budget that is going into it is quietly eroding margin with no visible warning.
Often both are true at the same time.