Hi Anonmyous,
One very typical mistake candidates are doing that they just think into one direction. What I mean by that that either they build their market sizing case bottom-up or top-down implicitly, without really thinking about those 2 fundamental options.
Ideally you generate an approach for both options and can triangulate both outcomes (should be somewhere in the same ballpark) or at least share the options with your interviewer and define together which way to proceed.
Jumping into one of those implicitly is definitely not top-down and not structured = not good in your interviews.
Hope that helps - if so, please be so kind to give it a thumbs-up with the green upvote button below!
Robert
Thanks! That is really very helpful. Appreciate the quick and comprehensive response!