Having experienced some annoying problems related to car rental and driving in the Yucatán, I hope this summary of issues to be aware of will be useful to other readers of this forum. (Some of these may also be relevant to other parts of Mexico.)

* PEMEX fuel attendant scam

Attempts by PEMEX fuel attendants to scam tourists seem
to occur with very high frequency (based on my own
experience as well as widespread reports on the web).
The two most well-known scams are not zeroing the pump
before starting to fill up, and switching a 200 for a
20 Peso note (after payment the attendant switches and
then displays the 20 note, requesting additional
payment). There is also a new scam, however, which seems
to involve surreptitiously stopping fueling and then
entering a large amount into the pump display claiming
that this is the cost of the refueling, when it in fact
represents the initial display for a new system allowing
the attendant to request a pre-specified Peso amount to be
purchased. (Look out for the pump displaying an amount in
Pesos, with no corresponding volume in litres, or a fuel
cost which is clearly excessive.)

Recommendations:
- Request a specific Peso amount rather than "fill it up".
- Keep a close watch on the entire refueling process (just
checking for zeroing of the pump at the beginning is not
sufficient). Ignore the sometimes blatant attempts at
distraction.
- Don't assume that a Peso amount displayed on the pump
represents the price of a completed refueling.
- When paying, pay close attention to the notes you hand
over, verbally counting out the amount as you do so.


* Rental car insurance

Mexican rental car companies frequently try to claim that
credit card CDW/LDW coverage is not valid in Mexico,
which is usually false(it's a good idea to confirm
coverage before departing for Mexico). Mexican branches of
large international car rental companies will usually allow
one to decline their insurance if one is sufficiently
insistent, but local companies may refuse to allow one to
do so. Worse than simply paying for insurance one doesn't
require, however, is the "10% deductible" attached to the
insurance offered by most of the local companies. This
deductible represents 10% of the value of the vehicle
rather than 10% of the cost of any damage, so that there
is effectively no coverage for anything except a major
accident.


* Rental car availability

During the busy period between Christmas and New Year, it
seems common for car rental companies, including Mexican
branches of international companies, to run out of
vehicles to the extent that they're unable to honour
existing reservations. It's highly recommended to contact
the local agency directly a day or two before the pickup
time to confirm that a vehicle will be available; if
informed that there is a problem, contacting the office
of the company in your home country through which the
reservation was made can be effective (this was my
experience with Hertz, at least).

An additional recommendation with regard to the PEMEX scam:

The PEMEX station in Tulum, just North of the intersection of Highway 307 and the road to Coba seems to have the worst reputation in the whole region - be particularly careful here, or fill up elsewhere (there's another PEMEX station a little futher North on Highway 307, for example).

Also, be careful about leaving anything of value in your car, even in the trunk. Rental cars are easy for thieves to identify, apparently.

We parked on the street in Chetumal while going to the museum there. (We had missed the parking lot entrance and didn't want to mess with one-way streets and going around the block - mistake!) After the museum, we drove to a big supermarket next to the Police Station to buy groceries.

When we opened the trunk to put in the groceries, our jaws dropped: the trunk was empty, except for a half drunk bottle of orange soda. Even the spare tire was gone! My husband's smelly old running shoes were taken. Fortunately our luggage was in the hotel that day, but most days it would have been in the trunk. We don't know if the theft happened at the museum or at the supermarket, but it definitely happened in Chetumal, not at an earlier stop.

The police took all our information for a police report - which we assumed we'd need for the insurance - then did nothing and let us cool our heels waiting for a hard copy of the report, which for some reason they could not produce until "mas tarde". We waited till we couldn't wait any longer - it was near sunset and we didn't want to drive back to our hotel on the Caribbean after dark. In the end, the credit card insurance did pay for the spare tire to be replaced. But the missing personal items were not covered, of course.

When we must leave luggage in the trunk, we always thread a lightweight cable lock (a ski lock in its former life) through the handles and then through the spare tire or the frame of the car. We don't lock any of the zippers. If someone breaks in, our hope is that they will rifle through the bags, but not take them (only to toss most of it in the bushes or the trash anyway).

Our valuables are always on our persons, or in a safe place, but who wants to spend their vacation replacing their toothbrush and underwear?