Ah so much grist for the mill here... I hate to think how long I have been busking, starting in the late sixties, as a ween... So, I have heard a lot if not everything.

I think both Ian and Alanabit are correct. I have heard that a huge busker's insult is to toss a small coin into a bloke's case. On the other hand, especially if there is a crowd not giving... and you don't have your case with you, priming the pump, so to speak ... is a great help, and I do pitch in in places I go...
I did toss a penny into a licenced busker's (scab) case who ran me off a spot in the subway by waving a licence at me and threatening to call the cops, fifteen minutes into my setting up...
As to holding spots... each town and city has a different tradition. In New York, for example, there are a large number of prime spots, but, a professional busker has to know where they are and when they are.

Once upon a time, the saygin didn't run you off from the front of the Broadway theaters. "Da" had just opened, so for an uilleann piper, it was heaven, espcially when Brian Keith took over from Bernie Hughes. Hughes was a lovely generous fellow, but every time Brian Keith would come to the theater, he drop a twenty in my case. At the time, seventies or early eighties, that was the equivilent of over a hundred today. Well, one day, after months of planing my daily circuit to be at the theatre about an hour and a half before the crowds started, a loud, and bad clarenet player set up at prime time, half hour, then the crowds started coming, right accross the street drowning out the pipes (uilleann pipes aren't too loud...)
So, I asked him if he could move to the middle of the block, the whole block was theaters... he began yelling at me from accross the street and a cop came and moved us both off.
It took me over a month to get back onto the block. I remembered the cops name, waited for him after his shift was off, and appologized. Turned out he was a police band piper... we remained friends for years... he died a few years back, great fellow.
Point is one has to work hard, and be diplomatic... in my book, be friendly to the state but maintain the soverignity of the tradition. Never give up the freedom that we gently keep in the light of the emergence of nation states. They are soveriegn because they are war like, violent and aggressive, we are soveriegn because we are gently persistant.

Thine, a freeborn man,
Lorcan
PS Bless you Eliza