Implementing or setting up pre-existing shopping carts depends on how the shopping cart is going to be used; and the set of products that will be used in the shopping cart; and depending on how easy you want to make it for the user experience, nine out of ten times this task will require some level of programming. If a shopping cart will be use for purchasing items where the item is extensive with detail, that affects how the price of the item is calculated or if the item has many options that also affects the price, and the pre-existing shopping cart will need to be modified to augment its current capability in functionality. Many issues will surface here if you have been given a project where you will need to modify the base code of the pre-existing shopping cart so you can augment its functionality to satisfy the clients need. Working at Dynamic Digital Advertising, I always have to go back to the base code and modify it or augment it to extend the capability of a pre-existing shopping cart. Example one of my project deals with a jewelry website where the back-end administrative functionality had to be re-written into what the client wanted. Many functionalities for reporting, order manipulation functionalities, add many features that didn’t originally exist for the products were augmented and implemented into the shopping cart. Also, I had to completely re-write the base code to achieve the level of usability for navigation, product display, product details and making the user experience easy and fulfilling.
Pre-existing shopping usually has the basic component but often a programmer will need to customize it to achieve what the client really desires.