Nearly every profession out there is not what your average layman thinks it is. I do not envy your task.
In this case drawing by hand is not a skill that is central to a graphics designer. Though it might be central to other designers such as industrial designers. But as a general rule you want to see the portfolio and choose based on that.
It would be much better if you only measured skills that you actually need. Do you really need hand drawing skill? If you do then you need to specify kind of hand drawing skill? This might lead you to hire a production artist or an illustrator instead.
But then if you really need a person able to sketch by hand rating that skill is not entirely straightforward. First there is a huge difference between a thumbnail sketch and a final rendering (which might take weeks to complete). This would be counter productive unless you need a hardcopy as many persons work exclusively digital.
Skills like this are not usually interchangeable. Ultimately drawing skills dont make a designer.