Then why don't you share with us what is wrong about it? It seems a fairly legit way to prove identity (I was thinking about it and the easiest would be to suggest the wrong number as directory services, hoping the person doesn't use DS and doesn't know the number that well, or is to sleepy to notice). Some parts are a little overdone, like, "Was Dave even his real name?" (of course not), but I don't know any better so instead of just making a short remark, why don't you share your wisdom?