National is famous for doing this; it is either feast or famine with their inventory. More so around any major holiday and or peak travel time.

Reserved a ICAR for Thanksgiving but when arrived was given a Chrysler 2000. Begged and pleaded for anything else but counter rep stood their ground saying "that was all we have".

Have always found best selection with consistent results in getting something *you* want is to use EA service. But around here that is only found at airports so there you are.