2 things.
As a seller, always take a video of your **** showing that it works while you state the date and the buyer of the item and then a brief video of you packaging the item. This will cover your *** so that you have proof it was in perfect order when it left your hands.
As a buyer, take a video of you unboxing and hooking up each item that you buy to verify that it works as stated. This will cover you as a buyer so that you can show that the item was defective upon you receiving it.
If this is done on both sides everytime, you will always know where the fault lies and it will also make it easier to file a claim with any shipping company