So you base your personal tipping habits based on the earning potential of a particular drivers proximity to the airport and the amount of people he could drive in a hour? And because he may have the potential to drive a lot more people you feel the need and apparent responsibility to ensure that he doesnt make too much, because obviously 20 an hour for a shuttle driver is just way too much. Do you tip the waitress at a low class diner more that you would at per say PF Changs? Bottom line, if you recieve a service you better pay for it, lest you be relegated to the gutter trash of society. And you hear some dumb FA telling her IOE student likewise you tell her to shut the hell up, the gene pool is tainted enough as it is.