Small secret, I tip everyone who does a little extra, or I tip to "get" a little extra. The tip can be a dozen donuts to the service guys when I bring my vehicle in for service. That got me 5 free injectors installed on my diesel Sprinter, mechanic said, as long as I was doing one - I did em all. Over the years being creative with tips and even tossing in cash every now and then has paid me huge dividends. I was in the service industry and to this day I remember each person that tipped me above and beyond, and I guarantee they also got above and beyond from me.
Learned that lesson from an old "mafia type" guy. He would walk in to the lunch counter and always tip $1.00 on a $0.25 cup of coffee, and all the waiters and waitresses would trip over themselves to pour his coffee before he even sat down, and his cup was never cold and never fell below a half inch from the top.
Yep gratitude comes back to you in spades.