Non existent support, and frequent issues. Do not use if you are a UK seller

I wouldn't recommend Shift4Shop for any UK vendors. The support is US-based so if you have an issue with your store during normal UK business hours you are unlikely to get help until late in the afternoon UK time. The sites often have issues. This can be as catastrophic as complete downtime (happened recently when they moved servers - downtime was over 12 hours, with no redundancy), or products not appearing because of a problem with their API (this happens frequently). Also, they seem to have a problem with VAT. For example, we have a product priced at £11.00 (inc VAT). However, when they calculate the VAT they have an issue with more than 4 decimal places so customers purchasing 4 items for example might get a final invoice for £44.04. I experienced poor customer service and we've had to customize the back end to deal with this. Overall the support (or lack of) is the biggest issue. This is an actual response I received when our 3 stores had been down for over 12 hours, resulting in lost revenue of many thousands of pounds: "Thank you for contacting shift4shop support team. I will be more than happy to assist you further in regards to your concerns today. Our server admins are in progress over a server migration and this is the reason the site is down. This migration is from 10pm to 10am est. Our server admins will work to get this accomplished sooner. Thanks and take care!"