I too have a Courtesy car which needed ad-blue as soon as I collected it from Enterprise.
I see it as a consumable much like adding fuel, and I’ll be returning it at roughly the level it was at. That’s the rule with fuel, so presume likewise for ad-blue.
The car needed new tyres from the get go too, as metal was exposed on one tyre & a slow puncture on another. Took it to Kwik Fit, and they changed all 4, along with tracking. They said it would have cost £1200 had I been a paying customer.