GA4 data is unreliable: how to fix it

Start with a conversion map

List the actions that matter: lead form submitted, call click, booked call, quote request. If a reported event does not map to a real business action, it is noise.

Common reliability failures

Duplicate tags firing from both hardcoded scripts and GTM.
Missing events on key forms and thank-you states.
Inconsistent UTM usage across campaigns.
No validation against CRM or inbox data.

Fix sequence that works

Remove duplicate or conflicting tags.
Define and configure conversion events clearly.
Test end-to-end journeys in debug mode.
Validate weekly against real lead records.

Reporting focus

Track qualified leads by landing page and source. Stop optimising on generic engagement metrics when your goal is enquiries.

Read GA4 data is unreliable for a problem-led version, and traffic up, enquiries down if lead volume is dropping.