When a customer orders a drink incorrectly I try to politely explain the correct way and phrase it is such a way as to make them feel like I’m making *their* life easier and ensuring they get exactly what they are paying for.

As a fellow Utah starbucks barista;
I find myself in the situation where LDS customers will become upset with me in regards to the refreshers, because they’ll sit there after getting in, wondering what’s in it that makes it caffeinated and then finding online the green tea extract. I personally find that the rules are super weird regarding caffeinated beverages in the church, seeing as they can HAVE them as long as it’s not coffee or any tea that isn’t herbal. I know churchgoers that like decaf but technically that’s out of bounds to them too.
Usually they all stick to frappes and I don’t have the heart to tell them that it is technically still coffee.
The mobile orders; I just ask them a couple questions and usually I can work something out.

Well usually we ask if they want any recommendations?
What do they say/do to show that they don't know about coffee? I actually just moved away from Utah (in the heart of the Mormons) I can't really think of examples of the top of my head