Yes, thanks, but I am already quite familiar with the idea that users will break and misunderstand any UI in creative and unexpected ways. That's why we do testing of any new UI designs. That's totally unrelated to my point.

My point is that the author writes as if something that is perfectly familiar to any mobile app user--and is literally the standard way to present a default option that can be changed--is something that has never been seen before. As I said, find me a mobile user who doesn't know what that arrow means in the screenshot in his article. He gave up all credibility with me at that point in the article. It may be that there's a story here, but either way this is just terrible journalism.

The way I read the article, the author is pointing out the sneakiness of 1. conflating service with tipping, and 2. hiding an option people assume isn't adjustable (who would think you could waive a service fee, and what normal person would want to pay a ~higher~ service fee? note that service fee vs. tipping has different connotations) behind a nav.

There certainly is a understanding problem here, even if the individual components are all familiar, because it's not at all clear what tapping a chevron on a "service fee" would do anyway, and it's certainly far from default to assume that that's how you would tip, especially if you were unfamiliar with Instacart, and didn't realize tipping is a thing.