It shouldn't be more complicated than selling alcohol to an adult, really.

Sixt gave me the car I reserved in 3 minutes time, half of which was me walking to the car, no upsale attempts, just a quick driver license check, some instructions regarding EV charging and here's your key sir have a nice day. That's how it should be.

If I were to steal the car, I'd bet they'd have no trouble tracking it down, as the technology involved is trivial nowadays.