There are no buskers in my small-ish city. When I travel, I always carry cash, and if the busker is good and not "phoning in" his/her performance, I always give. I don't give if they are too loud though because I can't support someone damaging another's ears.
But then, I'm a career musician. Making a living by playing music is getting more and more difficult in the USA, and I suspect other countries. I blame TV.
TV? When we were young TV was either black and white or later grainy color. and the sound was tinny. You had to go out to see and hear good music. Now we have HDTV with 7.1 surround sound and a cable bill that can easily top $300/month. There goes the entertainment budget.
I'm glad I was born in my time. I feel sorry for young musicians that don't have the opportunities that I had.
I've played in seedy bars, in concert with major stars, and every thing in between. I make people happy for a living. I'm lucky.
So when you pass that busker, give him/her some cash if you can. And turn the TV off and go to the night clubs where you belong
OK, I'm off the soap box now.