Key takeaways
- Most GA4 properties were created in a hurry and carry duplicate or unused events.
- Decide your conversions first, then audit events backward from them.
- Fix cross-domain and referral settings before you trust any channel report.
- Set data retention and link BigQuery early, because neither works retroactively.
Your team migrated to GA4 because Universal Analytics stopped processing data, the numbers look roughly right, and nobody is sure why some reports disagree with your ad platforms. That is the normal state of a rushed migration. The good news is that a focused cleanup, done in an afternoon or two, removes most of the doubt.
Start with the decisions, not the settings
Before opening the admin screen, write down the five to ten business actions that matter: a purchase, a lead form, a booking, a quote request. Every cleanup choice below flows from that list. If an event does not support a decision someone actually makes, it is a candidate for removal.
Audit your events
Open the events report and sort by volume. In most properties we see, three patterns show up: events that were recreated with slightly different names, events that fire twice, and events nobody has looked at since launch.
- Merge near-duplicates into one naming convention, for example lowercase with underscores.
- Check that recommended events, such as purchase and generate_lead, use the parameter names Google documents.
- Remove custom events with no owner and no report that uses them.
- Confirm that a single page load does not fire the same event from both a tag manager container and hard-coded script.
Mark conversions deliberately
In GA4 any event can be marked as a key event or conversion. Resist marking everything. Each conversion feeds reporting, audiences and, if linked, ad bidding. Keep the list short and tied to the business actions you wrote down at the start. Then compare the count in GA4 against the source of truth, such as your order system or CRM, for one full week. Small gaps are expected. Large gaps mean a tagging or consent problem.
Fix cross-domain and referrals
If customers move between your marketing site and a checkout, booking tool or payment page on another domain, configure cross-domain measurement. Without it, one visit becomes two, and the channel that started the journey gets replaced by direct or by your own checkout domain. Also review the referral exclusion list so payment providers and your own subdomains are not counted as traffic sources.
Set retention, filters and access
Event-level data retention in GA4 defaults to a short window in standard properties, and you can extend it in the settings. Extend it before you need it, since it does not recover data that has already aged out. While you are in admin, filter internal traffic, review who has access, and remove former agency and employee accounts.
Link BigQuery early
The BigQuery link gives you raw event exports that you own, which matters for custom attribution, joining with CRM data and auditing what the interface shows. Exports start from the day you link, so the earlier you connect it, the more history you keep. Plan for storage and query costs by setting a budget alert and partition-aware queries from the start.
- Write the list of business actions and map each to one event.
- Rename, merge or remove events to match the list.
- Mark only the mapped events as key events.
- Configure cross-domain and referral exclusions.
- Extend data retention and filter internal traffic.
- Link BigQuery and confirm the first export arrives.
- Reconcile one week of GA4 conversions against your order or CRM system.
