When treating one seller quietly hurts the control seller
A marketplace runs an A/B test: treated sellers get boosted higher in search results, control sellers do not. Treated sellers see more sales, control sellers see fewer, and the team reports a large positive effect from the boost.
Explain why this A/B comparison overstates the true effect, and how you would design the experiment instead.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.