If you're worried about giving the seller access to your credit card information, use an online service such as PayPal, which is safe and free for the consumer. Still, be sure to link that PayPal account to a credit card rather than your checking account. If a dispute arises and you can't return the item, you can recoup up to $2,000 through PayPal, but you'll have better protection through the card company.
You might feel more comfortable paying for defense against nasty surprises by funneling your money through an escrow service. This makes the most sense if you're dealing with a new seller who has yet to build a fabulous reputation, if you're wary about your credit card's protections, or if you're spending an amount of money that makes you nervous. Anytime you purchase an item, you pay the escrow service directly, plus a small fee. Once you accept the product, you notify the escrow service to release the payment to the seller. Only use escrow.com, which is overwhelmingly recommended by auction sites.