I am asking about faking screenshots to prove a transfer that did not existed. Not sure if the question could apply to other events.
Some people implied this in the traders lounge.
My point is that no proof of in game behavior can exist outside what can be visible inside the game interface. And if it cannot be faked, it's an OOC evidence that shouldn't be used at all.
That is, if I do something and lie about it, I should be able to get away with it and a third person who wasn't witness of the event shouldn't be able to know for sure what happened.