Zipcar is horrible.
I rented a car, and returned the car in good time (10 minutes earlier than the due time). However, zipcar insisted that I returned 9 minutes late, and charged me 55 dollars of late fee. ($50 dollars late fee + half an hour extra usage fee).
I called them, the customer representative insisted that i was late, and only waived me 27 dollars. I have no idea what happened to the rest of the money.
But I did return on time. I made sure to look at the time after I parked it and swiped my zipcard! Plus, nowadays, everyone uses cellphone whose time is sync'ed to the wireless carrier. So undoubtedly, I had the correct time.
I am going to cancel my zipcar membership.