It’s easy to be complacent when jumping into a new car but there can be plenty of things that may catch you out. I’m sure most people have gone for the windscreen washers in an unfamiliar car only to blind an oncoming driver with the full beams or perhaps momentarily stuck down a cul de sac on a test drive, unable to get the bloody thing in reverse. These little incidents can be amusing, but getting flustered at the wheel is never a good idea and in an emergency situation and this unfamiliarity could lead to an accident.
It’s well worth taking the time to get to know your hire car, where the controls are located (particularly things like fog lamps and hazard lights) and take the time to adjust your seat position etc. Drive a little more cautiously than usual and if you’re driving abroad, make sure you’re well acquainted with the local laws.