They caused me an inadvertant hardship on their website by saying the auto I had chosen was no longer available to rent but then charging for the insurance. This flagged my credit card company and they froze my account. When I got through to RentalCars.com the next morning they quickly cancelled everything, found that the car had actually been reserved (twice actually since I tried twice). They worked to get the money refunded quickly to the now-frozen account.
I will consider using them because they handled their error quickly and well.