I was picking up a reserved car from Europcar in Florence when they refused me as I did not have an international license. I had never been asked about this license on previous travels in Europe and Rick currently implies you don’t need one in Italy, saying “How this is enforced varies: I’ve never needed one.” Europcar said “it is the law in Italy” to have this license.
Other car rental companies were out of cars until I got to the Avis counter. They charged me 900 euros for three days, saying they were low on cars. This was 3X what my reserved car would have cost (for a better car). Lesson learned, always get the international license before heading to Europe.