Warning. This happened to me. Not far from the Ponte Vecchio today at 4pm.
A clean cut man from Barcelona comes up and asks for change for the phone. His car broke down. Then he asks for a 5 euro note for his other coins. While I root through my wallet he says, Oh, here. Points to some Canadian bills. Nope. Not Euros.
But my attention is distracted to that part of the wallet. I never do find a 5 Euro note so we give up. His English is poor so I really have no idea what he needed in terms of coins and bills.
A few hours later at a cafe, I look for the 50 euro notes I had gotten from the ATM. Sure enough, both are gone.
This guy was very, very good. A Sleight of hand artist.