I don't know what the MasterCard exchange rate is. However, someone recently told me regarding their credit card: "they give me the wholesale exchange rate, which is great". It turned out not to be so great (~1% wide market). It's good not to pay an additional fee/spread on top, but it can still be a poor deal overall.
Google isn’t really an authority. The Google rate could be bad and MasterCard 0.1% worse. They could be from different times. Also, the MasterCard site says indicative only - if I convert the amount back again, MasterCard claims they are giving me free money.
GBPUSD spot is 0.002% wide (so you’d expect to pay ~0.001% for a single, instant transaction up to several million). It’s not actually too difficult to access this through a brokerage.
That said, if you could really get 0.1% from them it’d probably be considered good at retail.
