I personally don't believe this is legitimate. The way clan wars is set up makes it so you cannot look at enemy bases and see their traps or cc troops. Spying circumvents this and gives an unfair advantage to the enemy. While it is something that can be done (and is done frequently it seems) it isn't against the rules.
Supercell either needs to make it possible to view traps and cc troops, or create more countermeasures to ensure spying does not happen. As it stands right now i do not feel the playing field is even. Our clan does not allow people to join because of this as it has happened to us in the past. So if it happens to you, then do not accept people anymore while your clan is in prep or battle day.