I guess, I would say, you should use your "gut-feelings." If something doesn't feel right, something probably isn't right.
http://www.cnn.com/2012/09/28/world/iran-news-agency-duped/
1) Whether we like the person (i.e., can we get along with him for months, years, etc.)
2) Is the person honest?
3) Was this person recommended, and do your views align with the recommender's?