If you go to a craft show or popup market or anything like that, every vendor has a Square reader to take cards. They're super successful with "offline solopreneurs" -- the independent one-person small businesses.
One of my many side gigs is selling laser-cut wood stuff of all sorts, and I make a set of Square Reader docks that sell really well. I just made several this weekend.
https://www.etsy.com/shop/ligninandlight?section_id=26787311