Zipcar will charge your credit card for no reason and would rather have you dispute with the credit card company than refund you.
I encountered this and thought it was interesting. If my company had charged someone and found there was no trace of it in our system, I would be very concerned. But at Zipcar they seem to play it off as not a big deal. I wonder how much revenue they make from randomly charging people who don't notice.
https://imgur.com/a/ET3ckK9