Originally Posted by
percysmith
This is completely untrue. The data referred to on that thread is many years old. The assertion that "In practice they can cherry pick worst rate within 5 days of posting date" is, in particular, completely false. See the text in the US T&C for current Amex credit cards, which limits the possible choice to the processing date or the previous business day:
The rate AEEML uses is no more than the highest official rate published by a government agency or the highest interbank rate AEEML identifies from customary banking sources on the conversion date or the prior business day.
UK T&C is even tighter, limited to a single day:
The exchange rate we use will be:
• the rate required by law or customarily used in the territory where the transaction or refund is made, or where this doesn't apply;
• based on interbank rates selected from customary industry sources on the business day prior to the processing date. We call this conversion rate the 'American Express Exchange Rate'.