The exact same argument applies to someone who steals an actual, licensed taxi, and I don't think people worry about fake taxi drivers when they get a cab.
I agree, but people are warned about unlicenced cabs and many cab companies in UK will send an SMS with details of the car - make, colour, licence plate number - when you book because there was a problem of unlicensed cabs with radio scanners taking passengers before the real cab got there.