Drunk cowboys tip more than sober travel agents.

This ^ has been my experience anyway, working the coat & luggage check at the convention center. The guys who sell horse tack and livestock feed attended a free concert, with a cash bar, at the end of their sales event. As city employees, we can't accept tips for hauling bags around (and some of them were heavy!), and it was a little hard to turn down the five-, ten-, and even twenty-dollar bills these guys proffered at the end of the night.

The travel agents were mostly women, and I bet they don't make the big bucks, mostly, and they didn't offer them either. But they were generous in other ways: they offered to share the free stuff they got at alcohol-free sales events, such as chocolate-covered macadamia nuts, coupon books, and tote bags. As long as the items were worth less than five dollars, we could accept them.

Both groups of people were really nice and almost always said please and thank you. 
In fact, working at the convention center is a reminder that, all things being equal, about 98% of people are nice. 
It's also a reminder that we're not all that bright... 

Working with the general public, I'd say bumbling ineptitude (say, trying to claim an overstuffed monster suitcase as carry-on baggage) is a more general, bigger problem for us humans than intentional evil.