Give you an example. Some of candidates for openings in my company claim they have extensive JSP experiences. I asked them to tell me a few library classes they have used in creating custom tages. 70% of them tell me they could not remember, that means they were lying. To be fair, I even more specifically asked them to tell me which super class they had chosen in writing custom tags. Most of them still could not remember..I concluded they have never written custom tags. My questions are not tough, but they can be a benchmarch for the candidates.
Some other candidates claim they designed some project using Rational Rose. I aksed them to draw on the board a class diagram for classes Car and Part, and specify the relationship of these two classes. Very soon, I saw who are really experienced in Rational Rose.