Amazon does something like this too, though I'm not sure of the percent. I just know that every time I select to pay in dollars, any change in delivery options will select it back to pay in euros, where the bank is.
I genuinely don't know if this is good or not, but the UIs insistence on reverting back to another currency after my initial selection leads me to believe that my initial selection hits them the hardest the most
Amazon.com does add a ~2% "currency conversion guarantee" fee when paying in EUR, on top of whatever conversion they use. I imagine that the average cost of that "service" to them is closer to 0%.
I genuinely don't know if this is good or not, but the UIs insistence on reverting back to another currency after my initial selection leads me to believe that my initial selection hits them the hardest the most