i've run into problems returning a weekly rental early. not only did they switch to a daily rate, they picked a very high one! if you don't keep for four days and enough hours to count as a fifth day, you will lose. since i ended up returning to the same destination later in the week, i should have parked the weekly rental in the airport lot! (i did once "nest" rentals--i put a weekly rental in an airport garage at DAL, flew to IAH, and rented a car there for a day..)

but, if you return a daily rental early, they'll charge your daily rate for only the number of days you keep. you could run into problems with a weekend rental with a thursday pickup--there is a minimum stay requirement that you must meet. in my case, i wonder, should i have called the "rental extension" desk and asked for a particular rate? will that work to avoid the walk-up rate?