That seems to be at odds with how Bitcoin works with the handful of large retailers that accept it. Reading online experiences, there are a subset where they order something at Overstock/Tiger Direct, the order does not go through, but the Bitcoins are sent, and they are told to complain to Coinbase. The alternative is I spend 5 minutes on the phone with a third party to issue a chargeback. ACH are also reversible by a third party (the bank).

Is my understanding flawed? How does a chargeback work when a third party does not exist and the protocol does not allow chargebacks.

Edit: Note that the merchant itself doing a refund is not equivalent. The important feature of a chargeback is that its a third party issuing it.