> Mastercard doesn't have a monopoly

Are we living in the same world? Visa+MC are a duopoly borderlining being a de facto cartel organization and handle the vast majority of all retail transactions in the world.

There is only one other payment processor (at least for cards) and that’s Visa.

The margins are extreme, but so are the barriers to entry. To build a new card network you somehow need to convince a bunch of banks and merchants to support your card network. Good luck with that.

The EU even forced Mastercard to allow others to start a card network running over their infrastructure, after they bought EuroPay. But it’s so hard to get people to actually use a new card network, that no ones actually bothered to try.

If Mastercard is doing it, why wouldn't Visa?

Also, I think it's important to remember but most of us don't go and select Mastercard or Visa, most of us don't care. We just use what the banks use. I suspect changing from Mastercard to Visa would be extremely expensive and it's a lot easier and more profitable to just pass along that to the customer.

The customer chooses the card, the retailer pays the fee. Other companies can't undercut Mastercard's fees because the consumer(the person making the decision of payment type here) doesn't know or care what the fee is.

> Other companies can't undercut Mastercard's fees because the consumer(the person making the decision of payment type here) doesn't know or care what the fee is.

You got the consumer part wrong. The consumer is the merchant, which can decide if they allow Mastercard cards or not. Same as many merchants don't accept Amex. It's because they don't like to pay the Amex fee. Same as many merchants don't accept Apple Pay or Android Pay or why some merchants only allow card payments for purchases of a minimum amount.

Merchants are the consumers and they decide what cards they will accept. Based on what cards they will accept consumers will be picky about which cards they want to have. For those exact reasons I have a VISA credit card as well as an AMEX because I sometimes can't use my AMEX, otherwise I wouldn't even have a VISA CC.

Very few merchants have the market power to say no to either Mastercard or Visa. It would prevent to many customers from being able to give them money. Which would then make it pretty tricky for the merchant to make money.

Also Apple Pay and Android Pay don’t cost merchants more to implement or use (assuming they have the HW, which any card reader from the past 10 years will have). The card network rules also forbid merchants from not accepting them, but of course rules don’t mean much without enforcement.

Finally there is really only one company that can undercut Mastercard, and that’s Visa. It’s only a question of time before Visa bump their fees, there’s no way they’re gonna leave money on the table for long.

You have your terminology completely mixed up.

In most of the US, credit card surcharges (charging customers a higher price when using credit cards than when using cash or debit/bank cards) are legal.

Is it also legal to charge customers a fee based on what type of card they use? A large number of customers have multiple cards anyway, so that would be a meaningful incentive.

Yes, many merchants charge customers more when they choose to use AMEX for example.