Your credit card, along with a few before, during, and after pictures of you in the cab should solve that problem.

As well as being linked to the person before you (for fines or something), I imagine you'd be able to send for another car, saying this one is too dirty etc. At which point it would be routed back to a facility of some sort.

Combination of financial and social prevention, automated surveillance and market segmentation will (relatively easily) take care of this. I don't see how it could be a showstopper.