When I rode the bus to work (dont laugh), I always had to wait in Downtown Omaha for about a half hour. I never gave the bum's money because 90% of the ones that asked were drunk or just plain scary. I usually just said "Don't got any cash on me. Just the bus ticket" and then he asked others and got the same answer
But usually I dont trust them. If one is nice enough, I'll give them a few dollars.