Once you have an idea of store, you can get to work with just a few clicks without spending a lot of money, if any. You have complete control over your site and can customize it as you see fit. This is very convenient, but it does not address the real goal of your site - driving a profitable business online. If you thought hitting 'post' is all you need to increase traffic and sales - you are unfortunately wrong.
Turning WordPress into a vending machine requires a lot of moving pieces. When you sell online, you obviously need a beautiful, easy-to-use, and secure site. But you also need an online business plan, don't forget about SEO, shopping cart software, payment gateway, social media, email marketing, and conversion rate optimization for long-term success.