After 3 bad experiences with Hertz Cancun, I feel compelled to write and to warn fellow travellers away from them.
I am a Hertz Gold member and have rented successfully from them all over the world, so this is down to the local partner who owns the franchise.
Bad Experience No. 1: Arrive New Years Even 2010/11 with a confirmed, guaranteed booking--no cars. No apology. On the contrary, I was told I could have a car in 3 days, maybe, and that I was a "sucker" for having believed I had a reservation.
Bad Experience No. 2: Arrive July 2011. Car is there as booked, but it is covered with dents and dings, is stained inside, and smells overwhelmingly of human sweat. No other car available. Hertz insisted on taking a $2,000 USD guarantee on my credit card to let me rent the car without buying their additional insurance at $50 US per day, which was more than my rental fee. When I returned the car, they both processed the rental charge on their electronic credit card machine as well as took an additional paper imprint which they insisted on keeping (normally this paper blank that has been pre-signed is ripped up and returned to you)...and they swore up and down that I would not be charged twice--will have to keep an eye on this one.
Bad Experience No. 3: I rented a car on behalf of 3 graduate students coming to Mexico to do work for me. The same guarantee is demanded. Not surprisingly, as students, none of their credit cards can handle a $2,000 charge. Hertz won't divvy the guarantee up amongst them either. In the end, in order to get a car from Hertz they have to take a new contract which costs the same for 3 days as did the original for 3 weeks. They are told by the manager on duty, an Australian chap, that they can just change the contract when they get to Merida. Not so. We all go in the next day to change the contract back to the original and Hertz won't do it. They won't now accept my credit card as the guarantee. In fact they want to charge a drop fee of $100 US even though they are keeping the same car--and want to charge a second drop fee when they return the car to Cancun
Stay away from these people, they are totally dishonest and not at all consumer friendly. In the past we have always used Executive Cars, a Mexican company, but they no longer have a location at the Cancun airport. They are good, though, and don't give you all the same awful problems. Enterprise has also been good and is at the airport. Shame on Hertz.