eCommerce

Shopify

Use 24/7 Support Staff, they have a live chat
Does cost $29/month for subscription to maintain site using their service
Choose theme carefully, there is a large switching cost to change themes after initial development to stitch pages together again
They offer domain registration and management but do not have email hosting. They only offer email forwarding, which is good for incoming mail to your domain but not outgoing mail from your domain

Shopify - It does NOT integrate well with Wordpress unless the client already had Wordpress for Business. Shopify allows you to customize HTML/CSS for each of their themes and has a plug-ins library with applications to serve many e-commerce needs, such as wholesale customers. We recommend the Customer Pricing application.

Also, check out WooCommerce plugin mentioned below in Wordpress section