I had a great conversation with one of my cofounders about this. First off, if you're only asking questions to a point where they are gameable then your questions aren't very good. The example I was trying to explain to him was that I look for 'aggressive curiosity' and wasn't sure I wanted to put that into the job description. He laughed and asked how far could someone game that as we keep asking follow up questions on any aspect of the discussion?

Sure, people prepare! But that's a good thing. We want everyone to do well.

If we sense they're doing something they've rehearsed a bit too much, we might push them to do it a bit differently. "What if you tried to do this by _____", just to make sure they can think on their feet.

Honestly, though, the best candidates for us are the ones who wouldn't try to game it. They hear the prompt, and are just so excited to show and talk about a project they're building that it's not a problem!