Let's suppose we are in an advanced stage of the recruiting process of a company and this question pops up. Also, this is a startup, so the interviewer is not an HR agent but the whole startup team (four members).
The truth is "yes", but I'm in an earlier stage with other companies; furthermore, I am genuinely less interested in the other companies' offers. However, I am not sure how to deliver that answer.
On one hand, I think it might give the impression of someone who is not focused on their particular company and is only trying to get a job. Also, in that case I don't know if it's fair to the other companies to name them. On the other hand, I think it may help give the sense of urgency needed to make the startup decide faster and to let them know that I am someone "marketable" who is not there only because it is the only chance he had.
Are there any general DOs and DON'Ts for this kind of question?