I took a recent trip to Merida with my family (four adults and one child). We had made a reservation, with confirmation number, through Hertz to rent a Dodge Durango (or similar) for our time in Merida.
When we got there, we were told that there were no cars. None. It didn't matter that we had a reservation. It didn't matter that it was 9:30 at night and we had no idea what else to do. The agent said, "Don't blame me" and refused to help us further. He actually laughed when we said we reserved a Dodge Durango! He said we'd be lucky to get any car. It was insulting.
Looks like others have had problems with Hertz. I'd recommend going with one of the other rental car companies. I'm not doing business with Hertz anymore, anywhere in the world (and we travel a lot). I realize it was Mexico and standards are a different down there, but every other company that we dealt with while we were in Merida and the surrounding area were helpful and kind and gave us their best service.
f Hertz can't hold their offices to a higher standard, they don't deserve the business anywhere in the world.