Technically MDR is payable by customer only, but most of the big merchants don't explicitly charge it to customers because they want you to think that you are paying the same price as someone else who pays through cash or debit card, also they want credit card customers because they are heavy spenders than customers who pay through other modes. All these charges are factored into the price of the product that you are buying. Only small merchants who can't afford to pay MDR, directly passes it to credit card customers.