You absolutely should clarify the business model. Often even if it seems that you just a bit misunderstood the model
I recommend asking two questions in one: How does the business work and what are the revenue streams? Why do you need to know the revenue streams? Because it's one of the most critical pieces in understanding the business model. An example is Oil&Gas with up-, mid- and down- streams that are completely different businesses. This is also the most common pitfall in profitability cases (the 2nd pitfall is the Mix)
Other questions to ask in the beginning of the case are:
1) Clarify the objective. Here make sure that your goal is:
- Has a time-framed
- Has / has no limitations
e.g. Should I invest 100k in this business for 1 year if I want to get 15% return?
2) Ask the questions that will help you build a relevant structure and remove ambiguity.
And remember, all these questions serve one purpose - making a good structure!