"A customer places an order containing products." What is the data?
Answer it out loud before you open anything. The value of the flags below is in comparing them to what you actually said — including whether you asked who uses it before naming what you would build it with.
The situation behind the question
The interviewer gives you one sentence — "a customer places an order containing several products, pays for it and may later return some of them" — and a whiteboard. "Find the data. Do not draw a schema yet."
What it is really testing
Whether the candidate can discover entities, relationships and state from plain English, decide what must persist, and see the snapshot-versus-reference question before it becomes a bug.