Strange, I sold a watch on ebay a couple of days ago and listed shipping to the USA only, and yet I had some guy from Italy bid on it. Needless to say I had to cancel his bids and block him.
I refuse to ever deal internationally. I will not buy from or sell to anyone who isn't located in the United States. It's not worth the hassle to me.
Two points relating to what you mentioned/experienced.
1. If a buyer was originally registered in any 'other' county outside the U.S. but.... is currently "living in the U.S. with a U.S. shipping address" in your case it was "Italy", the transaction will go through because his mailing address is somewhere in the U.S. but you won't know that until he wins and the auction is over, only then will it reveal/show you a U.S. address.
Your buyer for your watch... did he actually tell you it will be shipped to him in Italy?..... if yes, then you probably do not have "Italy" selected/check-marked as one of your "Will not ship to" countries, within your seller preferences area.
Sometimes someone bids on my items and it shows they are in a country I don't ship to... but their shipping address in the Ebay system is within the U.S. that's why the system allows them to bid, which is fine with me.
2. It's not enough to state "just in text" within your items description area: "U.S. sales only/I don't or I won't ship outside the U.S. what the seller MUST do to stop one or more countries from being able to bid on your auction/s is... you MUST go into your 'seller preferences'.. and go to the "blocked countries" area, then select ALL the countries you won't ship to, it's very easy, you just put one or more checks in boxes next to the particular countries.
The only countries I ship to outside the U.S. are Canada, France, Japan, Sweden, Denmark, Switzerland, Poland..
I used to ship to Germany but started to have frequent problems so I no longer ship there, I have no issue with Germany, just their 'Postal System'.
The worst offender is Russia where I absolutely will not ship to, as postal "pilfering" is rampant.