I play Spy and I know how to now who a spy is:
1. Dodgy: Spies tend to jump to dodge explosions and when walking they awoid your teammates not to bump into them
2. Bumping: Always bump your teammates if you can't go through them it's a Spy
3.Shooting and Reloading: Spies can't attack in diquese and it has a reload animation when the Spy changes weapons
4. Medic Spies: A lot of spies love playing Medic Spies cuz Medic is the most trusted Class in the team... Easy way to know Medic spies is by clalling medic and see if they respond but note that some real Medics will not respond as well as well as Experienced spies will look around and find the one calling medic backstabbing them
5. Pyro: Spies are weakest againts Pyro's every other class only has a weak effect on spies. Pyro is your choice of Spy checking and or other things
