Your Internet customers are looking for the padlock icon, "https" prefix and the green address bar in the URL window of their browser. This indicates the highest level of protection and verfication available on the internet. Customers are reticent to input their personal information into a shopping cart unless they are assured of the security of your website. You need an EV SSL Certificate to assure your customers they are safe doing business with you on your website.
The cheaper standard SSL certificates do not have the trusted green browser bar and indicate that your business has not been validated. Don't scrimp on the most important indication of saftey and security that your potential customers are looking for.