If it was just Topsy waiting on just Eva every single meal that would be easy to see. But when things get more transactional and less.. relationship-al there's less incentive to turn the other cheek. Even if you were nice to them and they started tipping better, somebody else benefits. It's hard to think "what goes around comes around" at such times, I imagine. That's why we have the tragedy of the commons.
Every service exchange is about relationship, not realizing it is part of the problem. If you can build that relationship the first time maybe they come back. The bar I work at is in an area of town that has been heavily gentrified over the last ten years. When the place opened it wasn't uncommon for blacks to scream obscenities at the patrons through the large bay doors of the place, after six years we have a pretty decent group of black regulars. Each of the black patrons was hard won with handshakes, remembering names and drinks and just getting to know each other. The perception that each transaction is just a one time game is where the tragedy comes in and people fail to connect.