Card payment sucharges banned in Australia from 2026

[SeaWolf]

Besides competition (where it exists), what is there to prevent a business dropping their credit card surcharge and replacing it with an administration fee, or processing fee, or similar?

There's regulation around this, called Minimum Total Cost.
Businesses must display the total price of a product or service as a single figure. This price must be the minimum total cost – the lowest amount a customer could pay, including any taxes, duties and unavoidable or pre-selected extra fees. This includes any surcharges or other fees which may apply every day of the week.

Note also the pre-selected extra fee. The business can't add on a "convenience fee" that's supposedly optional but you have to ask for it be removed. If they add it on automatically then it has to be included in the displayed price.
Optional extras must be included in the total price, if the business pre-selects these options for customers. ‘Pre-selected’ means the business will include these options – and charge for them – unless the customer removes them.

In terms of the card networks rules I think they just define it as any extra charge added that is specific to the card. I'm sure their lawyers would make sure the T&Cs wording would be water tight.