Revealing mistake: When Quinn is ambushed at his home one shot shows the female caretaker lob a grenade at him before he kills her. It falls to the pool. However, when it explodes, you can see that the explosion is above ground. A further shot shows the pool exploding after that.
Revealing mistake: During the shootout at Quinn's home, the underwater shot of Quinn diving in his pool, you see bullets dive directly down. This can only be possible if someone was directly on top of him but you don't see any bad guy anywhere near the pool or overhead for that matter.