If you want to sell stuff on your WordPress website, the hands-down accepted practice is to use WooCommerce. Not only does it work extremely well, and is supported by the folks at Woo, makers of this theme, WooCommerce is also completely free.
After spending more time than I want to admit fussing around with several plugins to add shipping zones to Woocommerce, suddenly the plugin is self contained with the functionality I needed weeks before!
At a recent gathering of the Vancouver Web Design Meetup titled, E-Commerce Shootout, the top three platforms were discussed: Woocommerce vs Shopify vs Magento. The winner depends on you and your client.