Consider a small biz in Aus. They have a terminal, currently...

Consider a small biz in Aus. They have a terminal, currently paying a flat fee + % of txn as a fee.
Smartpay come along and offer no fees so long as you do $10k (or whatever the figure) and charge the customer surcharge.

The SmartPay NZ biz (right now) consists of them owning the relationship, but they're not the acquirer. They now set themselves up as one, and offer those same customers a different deal (as above). The business pays nothing up front, but SmartPay increase their own margins by 1) becoming the acquirer and 2) changing the fee structure.

It'd be a lot like your ISP establishing their own network, then calling you up with a cheaper plan that increased their margins. Except they don't have to pay to build the network, as they've done it before in Aus.