Think I have just found an odd bug with the merchant geolocation. Just made a payment to a merchant in Hobart, Australia.
Australian zip codes are much like the US ones, just being a set of numbers. In this example, the merchant zip is 7004 (which is Australian for Hobart). The Starling app shows the location as Chalmette in Louisiana (which is zip code 70043). Payment in AUD has gone through perfectly, and at MasterCard rate.