Usually if someone has an encounter with a great white shark and lives to tell the tale, the only "proof" they might have probably comes in the form of some sort of injury, if anything at all.
Otherwise, they have to trust their harrowing story will be taken at face value and that any skeptics will keep their doubts to themselves.
But I think it's safe to say Danny McDaniel has all the proof he needs, and one newly gummy shark can certainly attest to that.