When Del is telling Denzil about Brendan's last job, the clock in the background goes from 1:30pm to 1:45pm and back again in between shots
When Del and Rodney arrive at Denzil's flat, the clock in the background says 1:30pm. After Del tells Denzil a lie about Brendan's latest job, the clock says 1:45pm and after, it changes back to 1:30pm
When Denzil's wife storms out of the room and slams the door behind her, you can see that the wall to the right of the door lurches forward under the pressure of the closing door.
Del and Denzil have been friends since their schooldays, so if Del really was an experienced painter and decorator, as he claimed, Denzil would have known this.