But in college, I discovered Miss Manners, and Miss Manners is wonderful because she gives RULES of behavior that, if followed, allowed me to act normally. I had algorithms to follow and the fall backs of "I'm sorry" and "Thank you", which always work. Which means I thank anyone I think is reasonable to thank, including bus drivers and cashiers and bag packers. I also don't ask for anything special, like "I"m a good customer, so don't charge me your delivery fee."
What happens? Usually, I get a smile and a "you're welcome" and that's about it. Which is all I look for.
But I have had cashiers NOT charge me for delivery, and deli guys slip me a little extra, or counter people upgrade my drinks without me asking. And today, instead of having to wait 3 hours or so for a delivery from a store down my street (usually not a problem anyway), one of the guys loaded my boxes onto a handtruck and took them right to my house, and up the stairs. I tipped him well, and thanked him, but he did it because he didn't think I should have to wait. I didn't expect it - I never expect it - but it's nice when it happens.