I rent over 60+ cars a year (domestic) for business and have noticed that alot of promotions are for a (2) two day mininum rental period. If you rented for two days and returned after less than 24 hours the rental car company has good reason to carge you for the 2 day period.

This is similiar to a two night hotel package that you reserve and then skip out after only one day.

There probaly was a higher (1) one day rate that you could have reserved.