If a website is currently using PayPal payment buttons to accept payments, then implementing PayJunction's QuickShop payment button can done with ease while obtaining better merchant rates.
For instance, just like PayPal, PayJunction has a "Button Generator". Simply create a new payment button for each item on the website and then replace the PayPal HTML code with the PayJunction payment button HTML code.
Quick Video: QuickShop Payment Buttons
The following video explains the PayJunction QuickShop payment button feature.