Of course busking is not begging, but I always liked the idea of it being part of the "underground economy" ~ that is, I detest the idea of paying permit fees or, worse yet, taxes.

If you do have to pay taxes as a busker, it should be in the form of income tax, where you're be able to deduct ALL your expenses (strings, reeds, etc. ~ if not instruments! ~ plus meals while out in the marketplace, a clothing allowance, etc.: anything and everything). A flat fee or percentage, like imposition of a sales tax, is hardly fair.