You are charged for what you reserved - for Emerald Aisle ("regular" Emerald Club members) you book and pay for a Mid-Size and are entitled to take whatever cars are in the Emerald Aisle - for Executive (and Elite) members you book FullSize (and pay for Mid-Size) and take whatever cars off the Executive Selection. Any upgraded cars parked in those areas are fair game to take as a free upgrade. In your case if the Expedition was in "regular" Emerald Aisle, you are entitled to take it regardless - if it was in Executive Selection, you were entitled to it upon the direction of the greeter.