Wish I had read the reviews first. Everything about "worst shuttle service" etc... is true.
I bought the tickets (they charge $7 one-way for anyone over the age of 3), and then when they saw I had cardboard boxes with me, they forced me to take a refund because they don't "carry freight". I said Southwest didn't have a problem, and how was I supposed to get all my stuff back to the hotel with three kids in 105 degree weather.
I get the impression that the drivers have a lot of leeway when picking up customers (kind of like taxi drivers), because he offered us the ride anyways, he said he would take us if we paid a good tip and he charged me for my son (who is 3 1/2), even though they hadn't charged for him at the ticket office.
I didn't haggle with him, but paid what he asked ($29 for the four of us plus an $8 tip for the bags), and I explained to him that they had only charged us for three people at the counter, so if he had to pay them something for taking us, make sure not to include the fourth person. Sort of like an extra tip.
After that, the driver gave me a piece of advice: rent a taxi van instead and save some money. If I was reviewing the driver I would have given him at least three stars. I think he was British.