But why can't you just ask for what you want without people automatically assuming you're stupid? If you care that strangers think you're dumb you have to adjust your behavior a lot and some people would rather just be genuine. Besides, the easiest way to not look stupid is to make up a reason that sounds reasonable (i.e. lying) to get what you want. This is what many (most?) people do. If they want the Apple computer that comes in the smallest package they'll make up a BS reason (i.e. flight luggage restrictions) in order to seem reasonable to the stranger who works at Apple.
The question is really what kind of person do you want to be? Do you want a person who habitually lies about unimportant stuff in order to accomplish goals? Do you want to be a person who is genuine but gets unfairly judged by strangers? Or do you want to be a person who justifies themselves to strangers in order to avoid getting judged?
If you think lying is wrong and seeking the approval of strangers is a bad habit only one option remains.
The writer conflates "the person at the Apple Store was trying to be helpful" with "the person at the Apple Store thought I was stupid".
Part of the job of someone working in a customer-facing, sales job is to understand what the customer wants. A sales associate at an Apple Store probably has dozens of interactions every day where they're able to help people understand the products better and enable them to make a more informed decision. That is their job.
Saying "I just want the one that's in the smallest box" makes you look like a customer that's in need of guidance and help, and someone who's probably going to have a bad experience with the product if they don't get it.
Getting irritated by a response that is trying to help just shows a lack of empathy. People are not robots and there is a really good reason that the "white lie" is a thing.
The question is really what kind of person do you want to be? Do you want a person who habitually lies about unimportant stuff in order to accomplish goals? Do you want to be a person who is genuine but gets unfairly judged by strangers? Or do you want to be a person who justifies themselves to strangers in order to avoid getting judged?
If you think lying is wrong and seeking the approval of strangers is a bad habit only one option remains.