I use this type of question as a way of exploring whether they take a strategic or tactical approach to marketing decisions. Far too often, the responses I received were tactical. They'd describe what they would do on Facebook (or whatever channel or tool I presented them with), rather than taking the time to step back and consider the situation before jumping to a solution.

The answer I would want to get to that question would go something like:

Well, before I can answer that, I'd have a few questions for you -- who, specifically, are you trying to reach and what, specifically, are you trying to achieve?