No, most of the ones in the city were I live, are usually nicely dressed and clean shaven.
Couple of experiences:
I went to an Albertson's once where I lived and while walking to the store, I spotted a bum at the door. He was getting some change from someone. Well, when I walked out, I looked across the parking lot and he was getting into his brand new van.
I also gave some guy a dollar in San Francisco once after he asked for change and he got all up in my face saying that he wanted change. Well, I got back into his face and told him to give me back my money, and he was like, "Ok, ok, calm down". I'm sure there are legitimate people in need of help but the ones I've encountered have not seemed so.