Meet them at industry trade shows.

This gives you the opportunity to see them in action in your field, how they present (in the psychological sense more than the sales step sense), and to spend some time in person with them.

After all, you can ask them to lunch or dinner after you've spoken with them for a bit at the show.

Find out their attitude towards the show: do they resent being there (why? If it's taking valuable time away from prospects they've already qualified, that's a good reason. If they're bored and the company told them they had to attend, that's a bad reason).

What do they like about their current role? Dislike? Look for a match-up to your situation.

Don't expect an instant leap. If they do, that's likely a warning--they'll be quick to jump from you, too, later on. Just give them something to think about...and let it work on them. If they really are dissatisfied with their current role, they'll get back to you.

People buy from people, and remember that you are selling something here.