Yes, I always have a handy maphack. BUT I only turn it on if
majority of the people in my team feels that an opponent is
mhing.
To find out if the opponent is mhing, perform a simple test.
On your maphack
Ping at the location of the rune. Observe the suspects movement. If
he immediately moves toward the location, its an obvious give
away.
Another method is to put yourself in a situation suspectible of a
backstab. Wait for the suspect to backstab you. WHile he is waiting
for an opprtunity to bs, keep still. repeatedly ping at his
location to everybody, if he makes a sudden exit, its an obvious
give away.