I generally let people know that I know they're lying and leave it at that. Maybe it teaches them to be better liars, or maybe it teaches them to not lie to me. In couples counseling I had said at one point that I was going to call out my AW whenever she tried to lie to me, because trust cannot be built on a bed of lies. She understood what I was saying, but at the same time it doesn't really change an addict's behavior when they are actively drinking.