The Tourney Logic website's storefront is very tightly integrated with PayPal. I was able to do it by using the PayPal SDK for ASP.NET. I have to say I am very happy with the results. The website shopping cart allows you to add products to a cart and go through a check out process. Once you get to the point where the website is going to ask you to pay for your transaction it redirects you to PayPal. After you login to PayPal and pay for the transaction PayPal then sends use an IPN (Instant Payment Notification) message. We take that this information automatically process it and confirm your transaction. Once your transaction is confirmed we automatically send you an email with your license key(s). It really is a very nice way for a small business to provide a transaction processing solution for a very low cost.
My only complaint is that it is very difficult to debug. The IPN comes back to a web address therefore I can't use debugging in ASP.NET. If anyone knows about a Windows based IPN simulator please let me know!
If you are interested in signing up as a PayPal merchant click on this link https://www.paypal.com/us/mrb/pal=69GQTBV9H6PCY and you will help benfit Tourney Logic by giving us a referal credit..