how would someone go about finding a good wing chun instructor? what traits should they look for? what traits usually indicate problems?

See this article:
what is a Sifu?
by Zopa Gyatso

http://www.webwingchun.com/html/home.php?pagelink=whatisasifu

:)

to try to simplify the answer, a good instructor of any MARTIAL ARTS subjuct should teach using the 3 E's, ENTERAINMENT, making the learning enjoyable, if you don't enjoy something you probible wont stick with it or gain much benifit from it. EXERCISE, you should gain some physical improvement from your training time. and EDUCATION, by education i mean you MUST walk away with real skills in the subjuct your learning, in this case fighting.
And all martial artists should have the ability to have some self-defense/fighting skills, otherwise all were learning is tae bo