The fee is paid by the customer. It isn't an externality. An externality is when the cost is paid by someone who isn't party to the transaction.

>The fee is paid by the customer.

No it isn't. It's literally against their TOS for merchants to add on a surcharge for using Afterpay.

And yet, magically and by the power of the market, the fee will still be paid for by customers. It isn't like the merchant has a non-customer source of income. The money has to be coming from them.

If you don't want to pay the surcharge, shop somewhere that doesn't offer Afterpay. Or somewhere that doesn't honour the TOS, I once got an extra egg in my soup for paying cash.

>And yet, magically and by the power of the market, the fee will still be paid for by customers.

Yes, by all the customers, including those that don't use Afterpay.

Which doesn't make it an externality, because they are still choosing to use the vendor. My favourite take-out place for a solid 2 years was the cheapest on the street and probably because they didn't support Afterpay or credit cards. The customer has all the power to avoid the cost if they want to.

They pay the Afterpay surcharge because they want a standard shopping experience that supports lots of different ways of paying. If they want to shop on price Afterpay will vanish from their view.