When you ask a person if he's a spy, the answer will always be "no" whether he really is or not.

If someone asked me if I was a spy, I would most definitely say yes.

What about double spys? They'd have to admit being a spy to both sides

Well, they are called Intelligence Officers now so they are still telling the truth.

unless their stupid in the head

Ackchually, the law requires them to admit they're a spy if you ask them specifically