Now and then someone will ask me if they can have my water. Last week a girl took my water and told me it was the best water ever (not sure how it was.) And I winked at her and asked her if I would get a 5 star. She said she promised me a 5 star and that she would rate me a 6 if she could. So that's my tactic now. I know most don't want to tip, so if they take a water or something, I'll joke about the 5 star or I'll ask them to rate me a 6 star and get them to laugh. When you mention it, it reinforces them to rate you a 5 instead of forget.