> The incentive for merchants to accept cards for payment is that it'll increase number of sales this is something that ive thought about a lot, because while it is strictly true in the short run it may not be in the long run. For example, i don't have any debt, but i use a credit card for everything. Why? It's become my default to use it.

I wonder if the same thing will happen with BNPL (Klarna, Afterpay). These are higher fee than credit cards (5-7%) because they bring in new customers. But, like with credit cards, savvy customers are starting to see BNPL as interest free loans (aka free money on the float, even better than credit card rewards), and it's possible that they become the new consumer results. Merchants are left holding the bag of paying 6% processing fees for everyone, even people who can afford it.