Hello @BProtz thanks for your post. The easiest thing I think you can do is create a coupon for FREE SHIPPING, and then promote and give that code to just your retail customers. It may be possible to do with with groups, but I'm not seeing an option to apply a coupon/discount to a group.
If you setup a coupon for free shipping, you could also use Square Marketing and send out an email targeted to that segment of customer. They'd be notified and reminded of your free shipping offer. I hope this helps with your question.
