The example that springs to mind is Spree (https://spreecommerce.com/). Spree itself is open source, but Spree Commerce make their money from support, implementation and premium offerings.
The issue with Spree is that they rely on Wombat for connectivity to other systems and Wombat is NOT open source, it's a hosted SAAS solution. So by choosing Spree, you are inherently locked into using Wombat as well.