SSL (Secure Sockets Layer) is the standard security technology for establishing an encrypted link between a web server and a browser. This link ensures that all data passed between the web server and browsers remain private and integral.
The shared SSL is not recommended for e-commerce / shopping cart sites, because customers expect to see your domain in the URL. And if you attempt to use your domain name with the shared certificate, it is not guaranteed to work. Even if visitors can see your site, the shared SSL warnings will make customers uncomfortable submitting their credit card information through your website.
Whereas Private SSL is intended for situations where the general public needs to access your site securely. Private SSL is preferred for protecting credit card information for e-commerce/shopping cart websites, since customers see your domain name in the URL instead of Hostripples, allowing them to feel more secure submitting their data.