@superball

Square is the easy button, but their take is pretty hefty, from what I understand and I think Square either doesn’t or at least didn’t offer to be Merchant of Record, so you have to deal with the tax situation for every polity where someone buys your books.

I had looked into Lemon Squeezy, which does act as a Merchant of Record so you don’t have the tax headaches but they’re more of a payment processor than full on POS, IIRC.