The credit card companies tell you that the merchant pays. Cost incidence doesn't work like that. If every seller in a fungible commodity market has the same additional cost, the price is going up by that amount.
Incidence is very much on customers, but (high interchange fee) credit card users are getting a rebate of most, if not all, of that. It’s the cash users who AREN’T getting a rebate, and thus the incidence is on them (and people using other low-or-zero cashback payment methods).
The incidence is on everyone. Paying 3% more or, for small purchases, >10% more is a net loss even if you get 2% back. Meanwhile merchants are increasingly offering a lower price for paying cash, and the ones offering that will generally have the same credit prices as the ones who don't, so paying with a card is paying 3%+ more to get 2% back -- and not everyone even gets 2% back. People with poor credit typically aren't offered those cards.
Incidence is very much on customers, but (high interchange fee) credit card users are getting a rebate of most, if not all, of that. It’s the cash users who AREN’T getting a rebate, and thus the incidence is on them (and people using other low-or-zero cashback payment methods).