I bought something on amazon the other week.
Ran a test to see if amazon are making extra in fx fees --
Paying by NZD, the amazon converted amount was $333.68.
I changed payment currency to USD, and checked my CC Statement a few days later....
xxxx 9 Sep 2016 OFFSHORE SERVICE MARGINS $6.86 11 Sep 2016
xxxx 9 Sep 2016 Amazon.com AMZN.COM/BILL WA $326.57 11 Sep 2016
Total was $333.43
Amazingly close. Amazon are being fair with their fx fees which is nice.