How do you make sure analytics data is trustworthy?

Show that you audit rather than assume, since most analytics problems are measurement problems.

• Verify the tracking works. Use DebugView and the Tag Assistant, and complete a real conversion yourself to confirm it registers correctly. Do this after every site release — deployments break tags constantly.
• Check for duplicate tags. Two GA4 tags on a page inflates everything and is common after a migration or a theme change.
• Exclude internal and developer traffic, and enable bot filtering.
• Configure cross-domain tracking if the journey spans domains, or you will see your own site as a referrer and every conversion attributed wrongly.
• Check referral exclusions for payment gateways, which otherwise break session attribution at the moment of purchase.
• Reconcile against a source of truth. Compare GA4 transactions against the actual order database. They will never match exactly — consent, ad blockers, and attribution windows all cause gaps — but the size of the gap should be stable and explainable.

Note: Documenting a measurement plan — every event, its parameters, and what it means — before implementation is the practice that prevents most of these problems. Mentioning it signals real experience.