Reign of the free market
It is important to know that there are neither any legal frameworks nor any other determinations (e.g. of companies) regarding exchange rates. Providers can decide on their own. Credit card companies publish the rate they use on their website. Changes appear on a daily basis. It is therefore important to constantly check the current exchange rates in order to avoid bad surprises.
For more information regarding money abroad, please read this article: Cash withdrawals abroad.