Gittin 3 - Why did we believe the messenger?
Earlier we said that a husband can divorce his wife through a messenger. As long as the messenger (who comes from overseas) brings the divorce document (Get) and states that he saw it being written and signed, the divorce can proceed.
But why do we believe the messenger at all? After all, we have a rule that there should always be two witnesses. And if you tell me that this messenger testifies to the fact of a woman being divorced, and that here one witness is enough, just as we believe anybody when he says that the food he or she prepared is kosher, then I will answer that this is not the same. About kosher food I have no prior knowledge, but the woman was known to be married, and now he is testifying to a change of status, an event, and two witnesses should be needed.
So then how do we believe one messenger? - The answer is that the Sages established this so that it would be easier for a woman to get a divorce and to re-marry. But you might have another problem: in the absence of two witnesses, the husband may later claim that the Get was forged. - That is exactly the point: since the messenger knows that he will have to testify in court that he saw the Get being written and signed, he will make sure that it is completely proper. If the husband later protests, people will believe the messenger and not the husband.
Art: The Messenger by Johannes Verkolje