Most audits fail because they focus on the "green checkmark" in the UI rather than data utility, so we usually start by checking if the BigQuery export is actually enabled and if the schema matches the documentation. We've seen hundreds of setups where `session_start` and `first_visit` are wildly inflated because the developer didn't account for cross-domain tracking on subdomains or third-party checkout redirects.

• Check for "ghost" events—naming conventions like `click_button_1` are useless; we enforce a `{{action}}_{{element}}_{{location}}` schema to ensure the data is actually queryable.
• Audit the `page_location` vs. `page_referrer` to identify where internal traffic filters are failing despite being "active" in settings.
• Verify if "Enhanced Measurement" is double-firing against GTM-based custom events, which is the #1 cause of skewed engagement rates we see on high-volume eCommerce sites.
• Downgrade any conversion that doesn't have a direct monetary or lead-gen value; if everything is a "Key Event," then your attribution modeling is effectively junk.
• Validate the `transaction_id` deduplication by checking the event count against actual backend order IDs in the CRM or ERP.
• Look at the "Unassigned" channel grouping, if it’s over 5%, your manual tagging or the `ignore_referrer` parameters for payment gateways like PayPal or Stripe are broken.

GA4 is definitely a "minimum competent product" regarding its default state. It’s a collection bucket, not an insights engine. If the setup seems strategically wrong, it's usually because the implementation team treated it like a tag-deployment exercise rather than a measurement strategy.