I had a rental from Alamo this December where the fuel gauge barely touched the full line. By the time we checked out, it had moved just above the bottom of the full line. I told the gate agent and she said she’d note it on the rental. I figured it was down 2-3 gallons. I returned the car with just slightly more gas and told the receiving agent all of the above. He noted it on the rental and so far, no further charge on the rental.