With all due respect to all of the answers above, nobody asked Wendy what kind of site she's building, the scale of the project, or any other details, and you can't answer the question properly without that info.
For example, though Wordpress is very robust and can support a wide variety of site types, it was not created as a purpose-specific commerce platform--it was and is, at its core, a blogging tool. Yes, there are plug-ins for just about everything now, but they are not ideal for all applications, especially when it comes to any significant level of e-commerce.
I have learned from hard experience that the more plug-ins and add-ons you have to use to get the site you want, the more can go wrong. It's like over-altering a garment. You generally want to start out with a framework that is 'natively' as close as possible to your basic need.
If the project is modest, mostly content driven, with some decent customization options and maybe a small e-commerce component, Wordpress may be a fine choice. But if Wendy is building a significant business and looking for a truly customized e-commerce site with a 'high end' flavor, it may not be her first or best choice. She would be much better served to go with a powerful platform that was built from the ground up as a shopping cart. There are outstanding open source carts like Magento, Zen Cart and many more. Most also offer paid enterprise versions for bigger/more complicated sites and for those who want or need vendor support.
Wendy, the main thing is to identify your application, goals, budget, and what you really need in a site. Then do your research. See who is using the platforms you're considering, check references if appropriate (I have made enough mistakes building sites for my business that I wish I had asked around before starting a few of them). And if you choose an open source product, make sure there is a very active community supporting it.