That is not true. There isn't going to be any "proof," but there will be evidence, in the form of "I zipped the bag up, took it to the airport, handed it over, no unusual forces applied to it between the time I zipped it up and the time I handed it over. I took it off the carousel on arrival, took it home, no unusual forces, tried to open it, discovered the zipper was damaged."

To somebody who believes that the OP observed accurately and completely and wasn't lying (and there's a good chance the airline falls into that category) that's convincing evidence.


The OP should describe what happened as fully and accurately as possible (and if I were doing it, I would consider and refute the possibility that the bag was overpacked or the zipper defective) and tell the story to Delta.