I currently am driving a car rented from Dollar at the airport in Dayton, OH. I reserved a FULL sized car, as I knew we'd have a 27" suitcase, a 25" suitcase, a 22" suitcase, a Vera Bradley Grand Traveler (qualifies as a carry-on, but it's big), two VB Miller bags (hold a 17" laptop and other stuff), my DH's computer bag, and three passengers in the vehicle. They had NO full sized cars on the lot or expected to be turned on the day we were renting. We ended up with a midsized Dodge Avenger, with no gasket in the trunk (so it was leaking) and a bald tire, with 60K miles on it. My DH went back in and said NO. They gave us the same model car only newer, with 22K miles on it. It took some creative loading, but all the luggage fit into the trunk with the exception of one Miller Bag.
I am not happy that Dollar didn't have the car I'd reserved (MONTHS in advance) when I needed it. The Avenger is sufficient, and they gave us a $25 discount off the really good rate I'd already had for the full-size (so ended up with a rate of $92 for the week), but we wanted the full-size vehicle for comfort. THis is a driving vacation... legs of 6-8 hours... and we really would have been far more comfortable if we'd had the vehicle I'd reserved. I contacted Dollar customer service and they basically said too bad, so sad to be you.