Implementing a web-site store for Topologika (UK educational software) using the Paypal payments system.
Topologika is an educational software company. I inherited a great-looking site build by Will Godfrey and worked on it's maintenance. Then, in order to sell products over the web, they asked me to implement an online store. Initially, we had an unfortunate diversion using the Kagi online store system, which turned out to be far too awkward for the task in hand (be warned!).
Instead, we adopted PayPal and it became rather easier. We looked at their Express Checkout option, because it links with their "Offers" system (stores on their own site) and sounded the swiftest solution. But we were disappointed to find that this still needed payments to be made through a PayPal account. Sticking with Website Payments Standard meant that the buyer has the additional option of simply entering credit card details on teh Paypal site, and no account necessary.
I also prepared automatic email to be issued to the buyer and to the merchant when a transaction is completed.
The whole task was slightly hindered by a somewhat complicated handful of legacy Perl CGI code intermingled in with the PHP, most of which needed to be preserved untouched.
If any future PayPal developers are reading, I can endorse the PayPal system almost wholeheartedly (and far superior than Kagi). My qualifications are that we uncovered a couple of strange bugs in the PayPal Sandbox testing facility. These had already been uncovered by other developers and were well-reported in forums for some months. So it is a mystery why PayPal have not fixed them. However, these were not at all fatal: in the Sandbox for instance, no automatic email is issued to the Merchant by PayPal, even though it is when you run live, and even though an email is issued to the Sandbox buyer.