If I'm trying to hire people, why wouldn't I want to "tip people off" to what I want? I'm supposed to lie and then trick people into telling me what they're really capable of? That seems ineffective.
Interviewing people about their experience is a traditional way to verify things. E.g. If I'm looking for someone who can solve hard problems I can ask for examples. If they're beginning programmer who just got handed tasks like "code this function"... they will have no good examples.
I can also explain a problem I'm working on and see how the candidate approaches it.
But writing job posting that hides the fact I need someone who can solve hard problems seems silly.