Don’t judge a person by the cloths he wears.
And here’s an example:
Syag Lchochma
said, on the Inspiration/Personal stories regarding Shidduchim thread (Link):
…One of the male counselors was a border of the director. They talked him into working for them at the last minute, for the month before he left for Israel to learn. He was in cut offs and t-shirts and I had no idea what his story was (I was dating BMG guys). As time went on I realized this guy was more “frum” than I thought and was shtarker than my friends and I…