While on assignment in Paris in 2018, I made an appointment at Lloyds of London and decided to take the Eurostar train through the “Chunnel” to London.
At the train station in Paris, I exchanged money. After boarding the train, I found that I gave $100 (U.S.) for the equivalent of $65 in pounds sterling.
The currency desk did not exchange dollars directly into sterling. It exchanged dollars for Euros and Euros for pounds sterling an 18% commission on each conversion.
I would pay more attention when we planned a recent trip.