Quite often, some people are ready to do anything to make an impression of being a certain type of a person that they actually are not.
For example, being asked for her first impression about Mr X, Mrs Z may say:
"He is a gentleman… (?)*"
*Here, I'm looking for a word or phrase which may express the idea that Mr X gives Mrs Z the impression of what she thinks an entirely, in all ways a perfect type of a gentleman must be. What I've been able to come up with so far is "from top to toe"/"through and through", which doesn't seem to match the usage standards in this context.
Some time later, Mrs Z may find out that Mr X, say, has the habit of biting his nails, or that wears the same pair of socks for several days, or something like that. So he wasn't what she had taken him for at the first glimpse.
In this regard, I'm searching for idioms or colloquial phrases for Mrs Z to explain why she took Mr X for what he was not. (I was thinking of "turn skin" or "werewolf", but I'm not sure whether they would work in the context.)