Cryptography can be used to maintain trust, not establish it. If there's no party checking who the driver is (in real life), having a cryptographic certificate

Cryptography can be used to maintain trust, not establish it. If there's no party checking who the driver is (in real life), having a cryptographic certificate isn't much of a guarantee apart from "it's the same guy it was yesterday". And if these certificates can be created ad-hoc, then you can always create a new one if you get a zero star review.