Google’s conversion count against the store’s actual orders, same window, before anything else is discussed.
Why first
Because everything downstream assumes it. Bidding optimises toward it. Reporting is built on it. Budget decisions follow it. Wrong at the source, wrong everywhere.
What we usually find
Over-counting from duplicate tags, add-to-cart counted as a purchase, missing conversion value, or post-purchase revenue never passed back.
What it changes
Sometimes an account that looked profitable is not. That is an unpleasant first meeting and a much cheaper one than the alternative. The detail.