I just want to throw it out there that Shopify Payments uses Stripe and charges 3% + $0.30 for every transaction, IIRC. Shopify Plus plans (which we have) see a reduction to 2.15% + $0.30 per transaction. I have never heard of any service which doesn't charge a processing fee. Paypal is 3% for normal customers, we're at 2.05%, so it's on a sliding scale as well based on processing volume. On other platforms, Etsy is the best at 3% + $0.30. Next is Ebay at an unwavering 8%. Amazon is simply the worst at 15% for most categories but will offer deals now and again. However, Amazon Pay is 2.9% + $0.30, if you decide to enable that payment method on Shopify.
(Please forgive my profile picture, it was from a B horror movie I was in. It must've come from Facebook and I don't know how to change it lol.)