Cancun car rental..ugh!
I just went to Playa Del Carmen for Valentine's Day. I rented an SUV from National over the Internet on car rentals.com. I was forced to pay an extra $20/ day for liability insurance and had a 2500$ hold put on my credit card. Annoying and smarmy, but not life-shattering or vacation-ruining. I would probably save the grief and buy it online at booking.
Longer version:
At the airport, I breezed past the timeshare guys claiming to offer transportation. I was met by National van driver and taken to rental place about half a mile away.
There, National runs a scam, and honestly? They have you a bit over a barrel if it is after dark and you are not real savvy re: Cancun. I go to Cozumel a lot, but it had been at least 5 years since Cancun.
Upon arrival, I was told that I could not rent the car unless I bought their insurance. In Mexico, the only mandatory insurance is actually included in the rental price by law. When this was pointed out, the counter guy shrugged and said, "meh, we are a franchise and our manager requires purchase of additional liability insurance or proof of coverage in Mexico." My US credit card auto insurance doesn't travel to Mexico, and I had actually looked in to buying a policy for Mexico, but could not do it without a residence there.
So, it was either walk away, try to hail a cab to go in the dark to playa del Carmen or couh up the extra dough for the 3rd party liability insurance for 20/day.
The only solace that I carried away was that 1) I called National and verified this was Mexican franchise policy, and 2) it was equally imposed against English and Spanish speakers.