Okei, From My point of View Wordpress is the best Platform for Developing an eCommerce website. Because CMS based Website are easy to create, processing, managing and presenting the content of your website. Generally eCommerce website's Content is changed on a daily basis according to the new products or new Arrivals.
I hated Wordpress (with WooCommerce) for a professional store with millions in revenue. It was a complete mess to work with, needing over 50 plugins to work together just to have what other ecommerce solutions already have out of the box.
Personally, I would only set someone up on Wordpress for ecommerce if they are selling PDFs or home made candles and no more than 40 or 50 orders a month. It's not for prime time.
I second magento. There are others OsCommerce, ZenCart, open cart, Agora cart just to name a few.
Here are some hints on the skill set requirements.
For Magento, you need to have at least basic knowledge of Zend Framework and strong OOP background.
For OsCommerce, ZenCart, Open cart, you need basic understanding of MVC design patterns and strong OOP background. All of these open source cart are pretty good and tested for years. OsCommerce have the most libraries and modules available.
For Agora, OOP background.
Another alternative is to build your own eCommerce system on top of well trusted MVC frameworks like laravel, Kohana, CodeIgniter version 2.2.0, Symfony 2, and Yii. For eCommerce application, I highly recommend Laravel, Kohana and CodeIgniter. The reason is that these frameworks already have a well established payment processing libraries. For example, CI can use omnipay.
By using MVC frameworks as the foundation of your eCommerce project, you are in control of the features you want your application to have. You can always add anything you want at any time. The only downside is that it takes a lot of work before you can see the final product. While in ready made cart, you don't have to do anything, except for features that you want to add. Besides, this can be built to be the ultimate eCommerce CMS if you want.