i am origonnaly form NYC. in my early teens i had tolearn the hard way how tip a cabby. and yes a few of them are self employed but almost all work with a dispatching company and have to pay a % of their fare to the dispatch. so the idea behind tipping a cabby is to kind of re-imberse them for the dispatching fee. so usually just go 15-20% unless it takes more that an hour then you go 25%. cause if you are holding them up for an hour they could have picked up two or three other fares by then. so if you are going a couple blocks you should walk. if you are going a couple miles use the subway. if you are going a cross town catch a cab.