As an online retailer it is you responsibility to provide each of your customers not only with complete security for all of their personal information and credit card data but with proof that you are making the effort to do so. The easiest way to do this is by using a certificate authority that can provide you with a digital certificate and the highest level of data encryption.
As you start looking for a certificate authority, you should be looking for find one that uses no less than a 128 bit SSL encryption program to protect all of the data being transferred. If you can find one that has several verifiable years in the business like Digi-Sign, you will find that you will be able to offer each of your customers the very latest in secure payment technology, this will give them the level of confidence needed to spend their money on your site.