Determine if they have a chip on their shoulder . Do they have something to prove? Where’s the hole they’re looking to fill? Ideally, you’d get someone with obvious talent/drive that is misunderstood by the world. Those types of people will run through walls to reconcile their internal view of themselves with external perception.
@mckaywrigley I have a bunch of questions I ask. What would you build for yourself? What did previous companies you've worked for need? What are you an expert in? What have you noticed recently that seemed broken? If you were going to build something just for fun, what would it be?
Using the collaborate before you commit approach empowers both the candidate and the person hiring, because they both have the agency to decide whether the situation feels right to them. Was there chemistry? Was there magic? Was it more awkward than you might have liked?