Trying to define specific logic and coding requirements need to give to the development team to implement. The overall process involves a consumer coming to the website, purchasing a product, being directed to PayPal, and then auto-returned to a receipt page that gathers the values and passes them to Google servers to be tracked as a successful transaction. I've referenced two Code Project solutions:
Is it necessary to utilize both PayPal PDT and Google Analytics E-Commerce tracking in a C#.net environment to properly gather the information from PayPal and fire the transaction in GA?
Furthermore, if it is necessary to use both solutions, can only the PDT portion of the solution be implemented or does the entire source need to be implemented and only the PDT and config files are altered as needed.
PDT isn't going to be accurate for you. Even with PDT and Auto-Return enabled there is still no guarantee the user will make it back to your final page. If they don't, the Analytics code wouldn't run and that order would not be tracked.
To remedy this problem, use the Express Checkout API instead of Payments Standard. Express Checkout basically consists of 3 API calls:
The experience for the user is very similar to Payments Standard, but they will always be sent back to your site prior to making the final 2 calls in the process. As such, you can rest assured that your final page will indeed get hit and your Google code will run and track accordingly.