There are a few key concepts to remember when investigating transaction discrepancies between Shopify and GA. The most important factor to remember is that in your Source Medium dashboard Shopify is your source of truth. This is important because GA can often be error prone due to a number of reasons:
- Ad blockers often times can block things like post-sell "Thank you" pages or points of references that signify a successful transaction.
- Misconfiguration of GA will often times fail to track or track additional transactions.
- ReCharge checkout issues are a very common issue that can cause transaction count discrepancies.
- Many other factors that are not visible to Source Medium can come into play.
It is reasonable to expect, generally, 10-20% discrepancies between Shopify (source of truth) and GA.
GA has no real way to distinguish between new and returning customers. This is because it doesn't have a total history of your new versus repeat customers, where as Source Medium has ingested historic data for your business. Using this historic data we are able to match a customer against those that have been ingested to determine if that customer is new or returning. A Shopify customer is someone that has placed an order with your business, where as a GA user is anyone that has started a session with your website.