Sex differentiation

Question
Books and other pamphlets are unclear: How do you tell the sex of a social finch?

Answer
A good way to tell is the blow on the vent of the finch (their bum) and see where the feathers are. A bird with long "feeler" feathers around the opening is a male whereas a female won't have that or any feathers in the surrounding area. This is of course just to make a guess. The best way to tell is to send away for DNA testing