Credit cards usually improve sales substantially . For example, according to many folks that have posted to the Link Exchange Digest, sales go through the roof when a site starts accepting credit cards. If you look through these postings , you'll see some very convincing testimonials. When sites add the ability to accept credit cards, they almost always see a significant increase in sales. People like paying by credit card.
Credit cards are easy to use, they are easy to understand, and they are highly familiar to people.
Similarly, credit cards can make the small guy seem big . The site feels more safe and secure . To some folks, sending money to a P.O. Box is just like burning it. It usually doesn't feel good to mail money away. Credit cards alleviate this fear.