Remarkety is actually more accurate in tracking generated revenue than Google Analytics is.
Google Analytics will only count a conversion when a user clicks a link and makes a purchase all within one user session.
Remarkety tracks purchases via email address rather than cookies, user sessions, etc. This allows conversions to be counted over a larger window of time and across different devices. By tracking via email address, Remarkety helps you to truly close the loop on a customer conversion.
To read more on how Remarkety tracks conversions, see here: How does Remarkety track conversions.