Didn’t show up at the airport to drop off the car we’d booked, despite our booking online and calling in advance to confirm arrangements. Very disappointing.
Update: about an hour after I posted this, Sixt’s (very friendly) staff called me with a sincere apology for the mixup, and arranged to have a car delivered to our hotel at no cost to fix the problem. They were super friendly, apologetic, service oriented, and made it right - which I appreciate very much.