Hiring for app design is different from hiring for a website, and most of the usual advice (check the portfolio, read reviews) misses the parts that actually go wrong on a real product UI engagement.
1. Ask to see states, not just screens
Any designer can show you a beautiful "happy path" screen. Ask specifically for an empty state, a loading state, and an error state from past work. If they don't have an answer, they haven't shipped a real product — they've shipped mockups.
2. Ask how handoff actually works
"Dev-ready" means something specific: named components, defined spacing tokens, and states your engineers don't have to guess at. Ask what the actual handoff file looks like, not whether they use Figma — everyone uses Figma.
3. Ask what happens when scope changes mid-project
It will. A vague answer here ("we'll figure it out") is the single biggest predictor of a blown timeline. A good answer names a specific mechanism — a weekly checkpoint, a change-request process, a capped number of revision rounds.
4. Ask what they won't design
Anyone who says yes to everything hasn't scoped the project properly yet. A designer who tells you upfront "that part needs a backend decision before I can design it" is one who's actually thought about how the product works, not just how it looks.
None of these four questions are about taste. They're about whether the engagement will actually finish on time with something your developers can build — which, in our experience, is the part that actually determines whether a product UI project goes well.