I hired a car from Alamo at Phoenix airport on the 3rd of May this year, and was stitched up by Alamo. 

Their agent attempted to sell us loads of options, when we said no to all of them he became very short close to being rude. He also tried to give us a lower level of car which I had to sort out at the pick up point (the lady here was very helpful).

However on return home to the UK and getting our credit card bill they had charged us for options we had not taken, such as a pre fuel charge of $43, not being aware of this we paid twice a we returned the car with a full tank.

We were also charged $231 for an additional driver which I had orginally requested through Rentalcar.com, but refused it when I got to the airport because they were running a promotion offering addtional driver free! I of course said no to the agent when he asked, saying I will take the free offer to which he made no reply and continued preparing the paper work for us to sign.

In total I got charged $363.95 for extras I didn't request. Alamo's response to date has been hard luck you signed now go away.  This is because of my final signiture on the last page.

Alamo's agents are clearly paid commission to up sell you and appear to be not to fussy how they do it.  I would suggest not using Alamo but if you do check the paper work before leaving the counter and don't get rushed through by the agent.