what is the recommended paypal (non pro) process when user purchases login credentials?

[eluser]WanWizard[/eluser]
Have you actually looked at the link I provided?

As first integration method, it says:
Simple integration - Use HTML to integrate Website Payments Standard with your website.

If you click on that, you'll find on that page:
Instant Payment Notification — Receive messages about transaction payments and activity from PayPal through asynchronous, server-to-server communication and automate your online payments with your order fulfillment process; requires advanced programming skills

Which in turn leads to https://cms.paypal.com/us/cgi-bin/?cmd=_...n_IPNIntro, which provides you your callbacks...