I think that part of D* historically has been a little flaky.
I was charged for a returned receiver a few years ago, had to call FedEx, get the name of the D* employee who received it to get the charge off my bill. They also charged me for a replacement receiver that replaced a unit that expired before the installers truck got off the property. Reversing that charge was quite a bit easier.
We do hear of the stories about those that got charged when the DVRs were returned, that has happened with both D* and E* at times. But it is an issue that should never happen! When you put that returned unit in the hands of the shipper THEY chose, your responsibility should end and that point. And in fact, I think it does end there and if they try to charge and you can show their shipper received it, I think they would back down from an argument.
In my case, I pay the bills with a very low limit credit card so that worse case they might get a very few hundred dollars, but in general I keep a balance on that so that there is only enough available to cover bills as they come due. That way if they want to recover some money they have to talk to me to get it.