Find someone who's been taught by them and ask of the experience. If that student happens to be similar to you in style/learning methods, then it might be a good fit. Word of mouth is best, I find.
I'd love to get instruction from snowolf, since having read so many of his tips, I already have a better sense of his teaching style and intentions. Too bad he's on the other side of the country.
SnowboardAddiction is a good one too, if you're good as self-learning.
Ryan - flickr