IMO it pays off - more than tipping - just to be friendly and kind. Some pilots do behave very badly, especially when the boss is around. I´ve seen that many times and I "wondered" why these get the fuel last, the catering is incomplete etc.etc.
I try to offer a sandwich or a candy bar or something and talk to the line guys just in the same way I want to be treated. If something goes wrong, I stay friendly and explain why I need this and that NOW.
However there is a fundamental difference between the US and Europe (I guess). In Europe I´m led to believe that the wages they earn are good enough to make a living, whereas in the US some of the guys have to have 2 or 3 jobs.