Your question is Measure Incremental Sales from Promotion. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You work on a consumer goods promotion test and see a sales lift during the promo window. The concern is that the lift may reflect pulled-forward purchases, pantry loading, or channel shifting rather than true incremental sales.
How would you evaluate whether the promotion increased true incremental sales? Explain how you would define the experiment, the primary and guardrail metrics, and how you would decide whether the promotion should ship.