Full Answer

GA4 mistakes cluster into configuration, naming, and ecommerce. On configuration, the classic error is assuming that because events appear in reports they are counted as conversions; they are not until you mark them under Configure then Events. Enhanced Measurement is often left off, so scroll, outbound click, and video events never register, and internal traffic frequently goes unfiltered, inflating everything with your own team's visits.

Naming is the quiet killer. GA4 treats event names as case- and space-sensitive, so purchase, Purchase, and purchase_event become three separate events that no report stitches back together. A short, lowercase, snake_case convention applied everywhere prevents months of fragmented data.

Ecommerce is where money goes missing. Purchase events without a unique transaction_id fail to deduplicate, so sales are dropped or double-counted, and missing item parameters leave product reports empty. Not linking Google Ads then starves bidding of conversion signals. The deeper issue is that none of these announce themselves: GA4 keeps showing numbers, and a typical client-side setup only captures around 70 to 85% of real sales anyway. The fix is to reconcile GA4 against your store's backend regularly, use Google's DebugView to confirm events, and treat any unexplained gap as a setup problem rather than normal shrinkage.