For most e-commerce sites, you absolutely need an SSL certificate! Your customers are providing you with very important and personal information that allows access to their hard earned money. If an identity thief gets access to your customer’s credit card information because you didn’t take the necessary precautions, it can be devastating to you and to your customer. Your customers need to know that you value their security and privacy and are serious about protecting their information. More and more customers are becoming savvy online shoppers and won’t buy from you if you don’t have an SSL certificate installed. As an online merchant, it is your responsibility to make sure the information you collect from your customers is protected. This will shield you and your customers by making sure that no one can intercept and misuse their credit card information.
If your site has forms that ask for sensitive, personal information you should be using an SSL Certificate. Otherwise, that data is transmitted in clear text. Not having SSL on your site could mean that you are missing leads due to visitors not filling out forms on unsecured pages.
If your site allows or requires users to login with a username and password then you should use an SSL Certificate at least on the login page. Without the SSL Certificate on the login page their passwords are transmitted in plain text and could be intercepted by hackers (even beginner ones) anywhere along the path from their computer to where your website is located.