A cautionary tale for people renting card

I rented a car from Woodford in Johannesburg, paid the necessary fees on collection and dropped the car off the following day. I do not generally examine my crcd statements (I know, my bad!) but perchance happened to notice an addiditonal charge of R2500 on my account. I called to query and only then did they send me an invoice - I had been charged for an additional 540km on my rental. I disputed the mileage and reverted with the details of the actual trips done. After 4 days of me having to call them for feedback, they sent me notification that I would receive the overcharge back into my account - no explanation, no apology - nada! How often do they get away with this? Lovely way to generate additional revenue! Since posting this message on Facebook, I have had a number of people responding with similar experiences so it certainly would appear that this is a fairly common practice.