As a consumer, I'd rather have the checkout complete on Amazon.com than on your site. First, Amazon.com has all my payment information already. Secondly, I trust Amazon.com more than I trust your site. I may be willing to give you a small amount of money, but I'm not willing to give you unlimited access to my credit card.
I think that's true for B2C, but if you sell to businesses, they probably don't have an Amazon account with their business CC on record. It also looks more "professional" to have the whole payment process contained in your site.
