I've been asked to do this for a couple non-tech founder friends. All I really do is have a fairly casual 20-30 minute conversation with the job candidate about

I've been asked to do this for a couple non-tech founder friends. All I really do is have a fairly casual 20-30 minute conversation with the job candidate about the state of whatever tech the product will be built in - "what's the quirkiest thing you've found in iOS?", "which backend platforms do you like? why that one instead of this one?", etc. Throw in a question about big O notation if you think this job requires some CS knowledge. It's generally pretty easy to see who can walk the walk, without resorting to grilling candidates with trivia or detailed hypotheticals.