Would that be a MITM attack then?
Sounds like one more reason not to use such services. You'll never know if the car that shows up is the one responding to the hail, that the car driver is the registered owner of the car, or if you're about to wind up as front page news when the driver turns out to be some psychopath in a stolen car that just carjacked the real driver & is now about to splash you literally across the next oncoming lorry they encounter.
Or am I just being paranoid?
*Tells The Voices In My Head to STFU*