Exactly. Of course, we do have to be a bit careful how we ask about past projects, to avoid the appearance of being exposed to IP, but it's doable. We can also just talk about hypothetical design problems (and they can learn about us based on the questions we ask, even if we're not doing a collaborative exercise). But no whiteboard CS101 coding negging.
When you're focused on system implementation, delivery and maintenance you can pick one of the past projects listed and start probing. It's not hard to quickly get a picture of what the candidate did and didn't do on the project and whether or not they're blowing smoke.