I’ve rented cars in Cancun on three separate occasions. A shuttle will always meet you at the airport and take you to a nearby rental agency.
My first trip to Tulum we wanted a Jeep, which is scarce due to the high demand. We used a Mexico based agency by the name of America Car Rental. Even though we specified a Jeep, they ran out and gave us an SUV, 2006 Nissan Pathfinder :/. The car was very shaky and in bad shape but it drove and we were able to exchange it for a Jeep once we got to the Tulum location. At the end of our trip we requested a discount, which never happened. They directed us to the corporate office, told us we’d have to file claims, send emails and of course we never saw a discount.
Second trip we reserved a car with Europe Car. Arrived at the rental agency and they ran out of cars….. so we got a complimentary ride to Tulum. The next day someone drove a car from Cancun to Tulum and requested that we drive back with them 2 hours to fill out the paper work and then drive back to Tulum. Of course we said no and cancelled the entire arrangement. I had to dispute the transaction with my credit card company in order to get my deposit back.
Third trip we reserved a car with Hertz and the process was beyond smooth. We landed, a shuttle picked us up, the paper work took less than 20 minutes and we were on the road to Tulum. I reserved a compact car and despite receiving a yellow car, everything else worked out well. We returned the car in with no random charges.
Tip: Use cash to purchase gas. Credit card theft is quite common at gas stations once they run your card. There is a gas station before you turn into the airport which has a reputation for scanning credit card numbers. My sister and I were both victims.