Thrifty Car Rental Deceptive Trade Practices Jackson Wyoming

Agent extended offer wherein I would pay for the first tank of gasoline and could then return the car without refilling it or paying to have it refilled.  The agent indicated that I would be charged only $3.68 per gallon while the prevailing prices were $3.85 per gallon.  That we passed a gas station less than 3 miles away that was selling gas at $3.74 did not bother me as I was still avoiding the hastle of getting the tank refilled before returning the car.  What did bother me and what I believe to be a deceptive trade practice is that they charged me for 18.5 gallons for that first tank when the tank (per the manual in the glove compartment) only holds 17.2 gallons.  In addition, at a point where the tank will only take 16 gallons, the driver display flashes an ominous warning "Refuel now to avoid damage to hybrid batteries."  $9.20 (=2.5 gallons X $3.68 per gallon) is not a lot of money to any one person, but how many suckers (like me) a day are falling for this deceptive trade practice?