At the moment of writing Sixt occupies a very small office in the ticket hall of Firenze SMN station. You collect the rental car on the -4 level of the station car park. It's usually very hard to find... BUT the staff came up with a brilliant solution: they shot a video of themselves walking there, showing all the elevators to use, all the directions to go, all the buttons to push, and they'll send it to you by WhatsApp if you pick up the car. It made us laugh and guided us to the car in less than 5 minutes.
Brilliant idea. Five stars.
Many thanks to Rico (Rica? Am so sorry to forget your name!) for the excellent and very speedy service today.