Most if not all transportation companies (and many other companies) have in their contracts that changes to the contract must be in writing and must be made by a corporate officer. Especially where there are lots of front-line employees involved in with complicated pricing.

Hertz: "... This, together with any of our policies referred to herein, is the entire Agreement between you and us relating to the subject matter herein and supersedes any and all prior or contemporaneous written or oral Agreements between you and us regarding the same subject matter (except other written, fully-executed contracts between you and us). Neither the course of conduct between you and us, nor trade practice shall act to modify any provision of this Agreement..." https://www.hertz.com/rentacar/navig.../legalView.jsp

Avis: "... Any change in the Rental Agreement or our rights must be in writing and signed by an authorized Avis officer..." https://www.avis.com/en/legal-documents/rental-terms

and for example, Delta: "... No Delta employee or ticketing agent has the authority to modify any provision of the Conditions of Carriage unless authorized in writing by a Delta corporate officer..."https://www.delta.com/us/en/legal/co...f-carriage-dgr