Buying SIM cards at the Auckland airport in New Zealand was offered DCC without any stated mark-up. A choice between $50NZ and $36+USD (don't remember the exact cent amount, I want to say 36.87 but not sure). The card transaction is listed as pending $34.53 right now, so mark-up must be anywhere between 4.25% and 6.75%. Buying a few items at a supermarket in Auckland paid with Google Pay, charged in NZ$, DCC not offered.