It's 2014, y'know
This whole eCommerce things has been around a while, folks, and there's some standards and best practices that can be followed if you feel like rolling your own shopping cart solution.
Please follow them.
Or better yet, choose one of 8,000,000 implementations of a shopping cart that exist now that do it right. Seriously, all you need is a map. Take your product owner, blindfold them, and have them throw a dart at the map. Whatever city it lands on probably has shopping cart software named after it. Go Google it, buy it, and implement it.
Manual removal of items
My wife's shopping cart session timed out while she had the gall to make dinner for our kids for 15 minutes. Did she get a warning that her session would time out? Do you even know what that means? So when she comes back to finish her purchase, she finds that all that time she spent finding the items is now wasted.
She had to manually remove each item... individually. Not even a
"Remove all" button. But that's not the issue. There should be
"Give me a new session (whatever that is because I'm a non-technical customer) and add my damned items back into my shopping cart" button.
Now she has to click a teeny, tiny 'x' next to all 22 items of the items in her cart, and then spend another 30 minutes navigating your site to find them all, pick the right size/color and add it back to the cart.
WTF is a credit card ID
There's this security number on the back of everyone's credit card these days. It's called the CVV number. Well, at least that's what every other shopping cart in the world calls it. You, however, decide to ask for a credit card ID number, and in your help section describe it cryptically as a 3 or 4 digit number above the signature line.
That's not helpful at all, escpecially if the credit card - like my wife's - has all kinds of numbers "above" the signature line. Here's a tip. Provide a picture. Then it becomes very disambiguous as to what you need.
Can't see my total until I've paid for it
My wife had two promotions to use on her purchase. However, she wasn't able to see exactly how much those promotion codes would actually save her until after she made her purchase.
Hello? Anyone home? People like to see how much money they are going to save with a discount code before they pay that money. Especially if they are trying to stay within a specific dollar amount.
You show database error messages to customers
This is just mind boggling in its incompetence. I went to your web site, found the first thing I could buy, clicked on the button to add it to my cart, and immediately saw this.