If you are in doubt, don’t be. Best $ I spent was to prepurchase RT transfers to the ferry for Isla Mujeres. They were waiting for me both times with new van and they took my luggage. There are so many local transport companies trying to get you to use them when you exit the airport and ferry terminal, it was nice to know I had rearranged this. I also prepurchased my ferry tickets for the family through them and was a real time saver. You should tip you driver each way (like $10 or 400 Pesos) but is still a great deal. There is no way I would drive in Cancun...they are worth every penny.