Hertz in Cancun is awful - I posted my experience on the Cancun master thread that is linked to the top of this thread.

That being said, it could be worse. The following week, a friend of mine received the bait-and-switch from a competing firm that had confirmed a $5/day rental. He declined and was then forced to rent from Avis. He received a car that broke down on the highway to Tulum. Avis sent another car with mechanics which he then commandeered and left them with the broken vehicle.