Woah.
That's insane.
Though OP, you should have not called Chase.
I would have just walked out (Good Lord, Rome has a lot of these people, doesn't it?!) and then once the charge posted, I would've called and said that I don't recognize the charge.
AFAIK, once a customer does that, it's upon the MERCHANT, to prove that the charge is valid or not.Atleast, that's how AMEX does it.
Or maybe AMEX is just plain awesome.
Off Topic- Try Rome in the winter. 90% less tourists. 90% less scams. 100% better tours. and 10000% better photographs.