WordPress Checkout use third party secure gateways to handle the payments.
- By default the plugin is integrated with PayPal Payments Standard. So, the buyers select the products in your blog but the payment transaction is completed on PayPal and you are making your post-sale decisions after a Instant Payment Notifications is received.
- You can customize the PayPal buyer experience with your own store look and feel. Visit PayPal Easy Integration Guide for detail.