I’ve only seen this method used once before at St Regis Saadiyat Island hotel in Abu Dhabi.

This time the naughty vendor was La Caserne Chanzy Hotel, (Marriott Autograph), Reims, France.

The final bill was presented in €. Mastercard inserted into card reader and € amount shown. PIN was requested and entered. No choice of currency was offered.

I then gave back the card reader. Then, after PIN entry for the € amount, DCC was offered in GBP (my card currency). Only because the front desk agent was honest and asked me, I could retrieve the reader and choose €.

I thought Mastercard rules prohibited post transaction DCC.

Contactless swiping avoided DCC everywhere else in Reims I went to.