It's not about "Whatever, here is your money back, just keep the device we don't care, goodbye."
It's about acknowledging the customers frustration, hopefully lowering it by returning the money no questions asked, and ALSO keeping the door open to continue the conversation in the hope for a more positive outcome.
Maybe the customer angrily throws the device away and you never hear from him again. Okay then, everybody moves on.
But maybe he is less frustrated and is willing to have a productive discussion about his problem, provide you with more information and try some things.
Again this might lead nowhere. Ideally you either find that something completely out of your control was the fault, and the customer can admit that blaming you for it was unreasonable, or you find the fault and are able to fix it.
So you might end up with a customer that no longer blames you, or even better one that is now able to use and enjoy your product.