People have a very difficult time keeping their story together, especially when they're asked a couple of questions that interview prep didn't cover.

Beyond that though, there's the probation period. If they can't do the job, they're supposed to be let go before they become permanent.

Trouble I see from most interviewers is a tendency of asking questions with a "right" answer. Those tend to be a lot easier to game. They then fallback on sorting applicants by pedigree - the old, "no one ever got fired for choosing IBM" method.

Then, they come back and rant about how PM's are trash, and Agile is trash, etc. etc.

Well if they’ve learned that much it’s a good thing.

The remaining piece is to speak with some personal references to verify they did some real work.