Paypal is my credit card processor, only you canít tell when you check out. It works seamlessly with the shopping cart software, so it does not go to any Paypal screens and the user has no idea that Paypal is actually processing their credit card. But just like any merchant bankcard account, they make changes to their interface from time to time, and the shopping cart software then needs to be upgraded to ensure compatibility. If I use a product that works with my merchant today, but then tomorrow the security settings change, or some other settings with the interface, I would need to get an update to the shopping cart software to keep it working. If I use software, I leave myself open to the possibility of designing an entire website that will only work for a short period of time, or having to pay for upgrades to the software to match the change in any UPS security changes etc Unless, of course, the updates to the shopping cart software free of charge, as well.