A small hotel in Spain. Booked through booking.com, but full bill to pay on checkout. Very clear € bill. Very clear € instructions given. Very clear € on pin machine. Charged in GB£. Disgusting print out from terminal - "0% commission over wholesale rate". Actually a 6.5% markup over mastercard's daily rate. Charge back effected via NatWest. No replacement € charge made yet, but I'm happy if the hotel does that. It was a very small B&B type place and the owner appeared to not be overly commercially aware, so it may be Banco Popular (the terminal provider) over charging, or the owner is a good actor.

ETA: The MasterCard charge back code is now 4834 - p.168
https://www.mastercard.us/content/da...back-guide.pdf