Almost every cab driver in New York acts unethically. As someone who lives in the city and takes cabs regularly, I can attest that 95% of them attempt to scam you in some manner. Sometimes they will take a longer route, sometimes they will add extra bogus fees, sometimes they will "forget" to turn on the meter. They will try and friend you to get extra tips. Very often, they will try and complain that the credit card machine costs them money (despite the fact that the TLC increased fares specifically for them). 20% of the time those credit card machines are "broken".
They almost always conveniently forget the flat fare rate from JFK to Manhattan. One time, I was in a cab and someone cut the guy off - so the cabbie sped up and started yelling at him - needless to say I was not amused. After telling a cab driver once we were making 3 stops, he refused to take us any further than the first stop - he was "on break".
This is an industry with a history of mob control and immoral behavior. If it takes GPS to help put an end to these things - I'm all for it.