Revealing mistake: When Frank ties the bedsheets together to the sink, he ends up pulling the basin off the pedestal. Surely that would cause a flood, but we don't see any water come out at all.
Revealing mistake: When Frank and Betty move the wardrobe, the walls wobble.
Revealing mistake: Before Frank pulls the mat from under the wardrobe and tears it, you can see the mat is already torn and placed back together.