Be sure to ask to be charged in euros and check before tapping your card. All across Italy on a trip last year we had been charged in euros so when paying with a credit card we didn't think to say anything. Then we went to Sorrento.
When settling the hotel bill the guy typed some things into a portable credit card terminal and pushed it across the desk, we tapped our card, done. Just as easy as all our other transactions. A day later organizing our receipts I saw we were charged a 3% convenience fee for being charged in dollars instead of euros. And printed on the receipt it claimed we were offered a choice of currencies to pay in. That did NOT happen. I never touched a button or screen, I just tapped my card. On a stay of a few days at Sorrento prices, between this 3% boost and the lousy DCC rate it was not a trivial ripoff.
This can happen anywhere, in a hotel, restaurant, or store. In our case it was Hotel del Corso in Sorrento.