I think that could be a valid question on its own. How you would approach this is to ask the client (Starbucks) a number of questions first.
I am no consultant, but have extensive practical experience within the aviation industry in general and Commerical is one of my key interest areas.
So if I assume Starbucks is your client and they are asking you this question then you would want to first ask them what is their client base in Beirut in general.
Other questions you may want to look into are things like what is the traffic and traffic mix at BEY, average spending on F&B at BEY, average time spent etc. As for a real case, I would dig quite deep and get all possibilities. However for a case study you don't have that much of data nor do you have that much of time, so to come to a quick conclusion you may want to quickly get or assume those numbers and compare them to the concession type offered to Starbucks at BEY and the fee, or profit sharing, they have to give to BEY. Well, even though if they have a good customer base and are still not able to match the costs at BEY then it might be pointless for them to open up there unless their motive is to market their product to a wider traveller base, market share growth etc.
Lemme know if you have any other questions.
Reference: Experience from working on major concessionaires at major airports in the Middle East and Asia.