Recently, a client showed me a report with a worried look: “Look, after setting up Consent Mode, our conversions dropped.” That immediately raised a red flag for me.

I opened the BigQuery export — and there it was: most actions were missing user consent. The conversions didn’t magically disappear. Users just weren’t giving permission to be tracked. In theory, GA4 should step in and model the missing data.

But it wasn’t. Why?

Let’s break it down — without the marketing fairy tales.

When a user doesn’t give consent for tracking, GA4 tries to “fill in the blanks.”

It studies how users who did give consent behave and guesses what the others might have done.

It’s not lying — it’s polite guesswork. But guesswork is still guesswork.

Here’s what you should know about modeling:

• It only works if certain conditions are met: Consent Mode must be properly implemented, and your property needs enough traffic — at least 1,000 consented events and 1,000 unconsented events over the past 7 days.

• It works differently depending on where you look: in standard GA4 reports, modeling only applies to big-picture metrics like users and sessions.

• It’s really hard to tell where modeling kicks in. Sometimes there’s a tiny flag hidden in the report setup saying “modeling applied from this date.” But spotting which specific data points are guesses? Good luck.

• Some reports don’t use modeling at all. Audiences, cohorts and a few others rely only on real, observed events.

• BigQuery doesn’t include modeled data. There you see the good, the bad, and the ugly — real data with all its gaps. Honestly, I’d rather deal with a few holes than stare at a perfectly fake story.

How I work with modeled data:

I always double-check whether modeling is turned on in any report. And I treat BigQuery as my source of truth — because there, at least, you can clearly see what’s real and what’s wishful thinking.

Bottom line:

You can trust modeled data — but only like you trust a weather forecast.

Helpful for planning, risky for betting your company on it.

GA4 isn’t lying to you. It’s just… a little shy about telling you when it’s making things up.

Real analytics starts when you can tell the difference between facts and fiction.

If you work with GA4 to BigQuery exports, be sure to check out my SQL cheat sheet.