How the duplicate happens

This is rarely deliberate. It usually happens in stages: a Google Ads conversion tag gets installed early on, then later a GA4 property is connected and its ecommerce purchase event gets imported into Google Ads as a second conversion action — often by someone who didn’t set up the first one and doesn’t know it’s there. Both get left as primarybecause nobody explicitly decided which one should count. Google Ads doesn’t warn you when this happens; both actions report normally, and the account’s conversion total is simply the sum of both.

What it does to your numbers

If two actions overlap heavily — say, the volumes are within a few percent of each other and the timing lines up hour to hour — the account’s reported conversion count and conversion value are both roughly double what actually happened. Reported ROAS follows the same inflation. An account showing a 4.1 ROAS with the duplicate in place might be sitting closer to 2.1 once it’s removed. That is not a performance drop. It is the same performance the account always had, measured correctly for the first time.

The more expensive part isn’t the reporting — it’s what Smart Bidding does with the inflated signal. Campaigns and ad groups that happen to generate a disproportionate share of the duplicated conversions look more efficient than they are, and bidding shifts budget toward them. The algorithm is doing exactly what it’s designed to do; it’s just being fed a number that doesn’t correspond to twice the revenue.

How to check for it

In Conversions → Summary, open each active primary conversion action and compare volume and timing against the others. Two strong signals of a duplicate: conversion counts that move together almost exactly week over week, and an hour-by-hour correlation that’s close to 1 — both actions spike and dip at the same times because they’re firing off the same underlying event. A genuine second goal (say, a newsletter signup alongside a purchase) won’t show that pattern; the volumes and timing will move independently.

Fixing it without breaking bidding

Once you’ve confirmed a duplicate, mark all but one of the overlapping actions as secondaryrather than deleting them outright — you keep the historical data and avoid abruptly changing what campaigns using target ROAS or target CPA are optimizing against. Expect reported conversion volume and ROAS to drop immediately after the change. That’s the fix working, not a new problem. Smart Bidding strategies typically need a short relearning period afterward, since the signal they were trained on has changed.

The broader point

This is why conversion tracking checks come first in almost any credible audit process, including how Ads Audit orders its own rule categories. A duplicate primary conversion isn’t a cosmetic reporting issue — it’s corrupted input feeding an automated system that makes real budget decisions every hour. Fixing it doesn’t just correct a dashboard number; it changes where the algorithm sends spend next.