Great question — answering as the UphillTech team:
eCommerce solutions are akin to encryption routines: you should avoid writing one unless you have experience building one and really know what you are doing. Especially in today's environment, there are many legal problems that have to be addressed in building your eCommerce solution that will protect your client from lawsuit. PCI and PII come to mind. It is easy to do shopping carts wrong and cause a serious amount of grief for your clients. By using a third party you, in effect, greatly expand your development team. You now have a whole company working on additions and updates to the shopping cart for you. A good shopping cart suite is extensible and allows for replacing components in the...
Full answer by Thomas: https://stackoverflow.stackexchange.com/a/2615418 (CC BY-SA 4.0).
Need it done for your business? UphillTech.