Unlike most people who mechanically give a $2 tip to a waitress who brings 2 tiny bottles of water, I prefer to tip people who don't expect it. I tip the cleaning person who cleans between the machines (although I never see anyone else follow my lead). The other day I offered a tip to a cleaning lady for the 2nd time, and she said that I had already given her before. I told her that I knew that, and that I wanted her to have it. Of course she thanked me (sincerely, not mechanically).
Last week I asked a mechanic who repaired a machine next to me if he could accept a gratuity. He declined.
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