> Where are you located that visa and MasterCard are charging 3%?

I am guessing the good old unregulated free market of the US of A: https://www.valuepenguin.com/what-credit-card-processing-fee...

There, banks and credit card companies offer huge perks and cash-back to card holders. That money must come from somewhere, and that's from the transaction fees paid by merchants (and transitively customers, as merchants still need to make a profit). AMEX has even higher transaction fees, which is why some businesses don't accept it.

The situation is now at an idiotic local maximum: if I don't use one of these cashbacks cards, I am losing money paying for my neighbor's air miles, as I don't get a discount anyway. You don't need a "technofix" for that, you need regulations that cap interchange fees like the EU.