When Ken strikes Don from behind the latter is seen to fall down on the bed, but in the next frame he is already lying face down on the bed.
When Tracey goes into a phone-box, the action of the door is quite unlike that of the solid heavily-sprung real thing, showing that it's a fake one..
The door of the safe bends inwards as Tracey presses the explosive into the lock. Confirming it is a prop and not the real thing.
Tracey's involvement in the robbery is supposedly discovered by the police when he pulls out of his pocket the other half of the drill bit discarded at the crime scene and tries to strike a light with it. It would be impossible to hold a drill bit and mistake it for a match.