I am going to have to disagree on the advice to ask the same questions of a consultant that you would a new hire.

A new hire is a (hopefully long-term) investment. One thing that you should want to decide is how well you think this person is going to learn. A person who will learn what you need them to know and then continue learning is worth far more than a person who just knows what you are working on. I would, and have, recommended someone who didn't know Perl over someone who did for a job as a Perl programmer based on how well I thought they could learn.

A consultant is a return on someone else's investment. You do not expect to get a long-term return on anything you put into that consultant's skills. You may have to train them, but you should regard that training as a sunk cost. So the entire aspect of whether you think you can train them becomes very secondary. Even if you can, you don't want to. Do they already know what you need them to?

Neither of these positions is, of course, absolute. Permanent employees go elsewhere, and you tend to work with a consultant for a while. But it is something to keep in mind.