It's highly unlikely that it would chomp down on anyone's hand. Possums are docile to a fault. Not saying it can't happen, just that it most likely won't. Good eatin'.
BTW, possums are NOT vermin. They are a very beneficial animal. Not beautiful, not glamorous, but useful. Vultures are butt-ugly too, but I'd hope the folks on this forum would have more sense than to kill them senselessly, too.