Online Merchants for Shopping Cart

There are no doubt, plenty of studies on what checkout solutions should be used for an eCommerce site's shopping cart.

There is the camp that embraces services like PayPal and GoogleCheckout that provide a (hopefully trusted) layer between you and those you exchange money with.  Some of the advantages of doing so could be viewed as:

Online Merchants; Middle Tier Services over Traditional

1. not exposing your raw credit card or banking information with every transaction.  You provide a username/password and these services handle the encryption and authentication on their own.
2. who hasn't heard of PayPal?  There is a reputation there that you can bet will be protected since there is a huge userbase
3. it's very, very easy for developers to link to most of these services, and you don't even need to personally worry about encrypted communication; again, these services do that for you as well

Perhaps some drawbacks to this middle tier service approach is that

1.  some require you to establish (yet another) a username/password.  Some offer the option of putting in your credit card information directly, just like with a traditional online merchant service
2. it may cost a little more than the traditional online merchant service option

Middle Tier Services
https://www.paypal.com/home
https://checkout.google.com

Some Traditional Services
http://www.trustcommerce.com/
http://acquiring.elavon.com/acquiring/costco/