In future I will take such a photo rather than just keeping the receipt from the gas station, but at the end of the day do I really want to be doing business with a company that attempts to rob me? Absolutely not. I shouldn't have to go out of my way to prove I filled up the tank if the business is honest. I mean they could just as easily say I returned the car with no wheels because I can't prove I didn't.
This is a company that has full access to my bank account. The least I would expect is an email to say why they have withdrawn money a week and a half after I dropped off the car.