Bottom line: overall I’m happy and everything went smoothly. I only had a translated license, no IDP, so they made me buy full coverage before they’d give me the car (full insurance was 150 PLN per day, but considering how cheap the rental itself was, it was still acceptable—and I didn’t have to wash the car when returning it). I’d booked a Mazda 2 but got lucky and was upgraded to a small Nissan SUV instead.

When you pick up the car, make sure to carefully check for every scratch and dent, take plenty of photos, and point out all the damage to the staff on the spot. That way you won’t get hit with unfair charges when you return the car—stand your ground if you have to.