Why should you pay for a remotely hosted shopping cart for your small business website, rather than just install a free OpenSource shopping cart on your site?
There are a lot of reasons:
Focus. Your business is selling, not installing and managing a complicated scripts. You'll have enough issues running a business that you won't be able to outsource to someone else the way you can with a shopping cart software.
Price. Paid hosted shopping cart software's price is inconsequential: $10-$100/month. If that's a significant expense for your business, you need to look into improving your profit margin.
Support. While support for "paid" business software is included in the cheap price, support for "free" business software is pretty expensive. OpenSource and other free software come without any support except forums for do-it-yourself-ers to share ideas.
Installation. When you buy hosted software on a subscription plan, installation is already done and support is included.
Security. Security issues are taken care of for you by the provider–no patching software.
Speed. Hosted online shopping carts really do work now, out of the box. You just input your inventory and go. OpenSource shopping carts come with dozens of customization options that will take you hours just to decide you don't need most of them.
Peace of mind. The shopping cart is the jugular vein of an online business. If anything makes the blood stop flowing, however minor the cause, you'll feel it fast. If you have to rely on the availability of a freelance programmer, you won't be getting the soundest sleep. Let a specialist do that worrying for you, 24 hours a day.