How do you trust an AI’s design layout when you don’t know design theory?

I’m not a designer. I build landing pages by telling an AI what aesthetic I want and letting it generate the interface. It’s magical, but it has one hidden trap: I can’t tell if the layout actually makes sense to a user.

A few weeks ago, I had AI design a sign-up flow for a mini project. It looked modern, sleek, and worked smoothly on my laptop. A week later, when I watched a friend try to use it on mobile, they couldn't even find the submit button because the contrast was terrible and it was buried off-screen. Nothing looked "broken" to me at first glance, so I almost missed it.

It made me wonder if non-designers are launching products too easily just because the preview looks pretty.

How do you test UI/UX when you can’t evaluate the design code or principles? Do you run blind user tests, ask the AI for accessibility audits, or just hope visitors figure it out? And has a "perfect" AI design ever failed you in the real world?