My experience was that buskers who *ask* for money did the best. I was always more of a background music busker, but I observed that folks who would sing a song or two, gather a bit of a crowd, and then actually pass the hat got more dough. Helps to have a gimmic or some patter, though. I remember a bluegrass band that played at the Hyde Street cablecar turnaround in SF (ever run into them, PoppaGator?) in the 70's; they'd rip through a couple of numbers for the crowd waiting for the next car, then pass the hat, with this set up: "If you liked what you heard, then give. If you didn't like what you heard, don't give. But in either case, DON'T TAKE!!" Worked well for them.

The real key to busking success is the same as in real estate: location, location, location.