Margaret and Borachio, are you completely sure?

In the plot Don John and borachio, do a mischievous plan in
order to deceive claudio and the prince that margaret
was unfaithful. The plan is that boraccio will hook up
with margaret at heros room so that claudio witness
it at the window, believing it is hero and borachio.
But, how can we be completely sure, what gives us the
certainty that it wasnt margaret and it was actually hero
that ho

Margaret and Borachio, are you completely sure?