Speaking as a performer/entertainer - my repetoire is pretty limited - and a lot of what I know the audience DOESN'T - so I can usually and honestly answer - "Sorry - don't know it".

speaking from the audience side - I *try* not to request anything - but some performers are kind enough to *ask* - and in that case I usually give an honest reply - what *I* would like to hear *them* sing/play.

So it was with great pleasure I got to hear Seamus do Jed's 'Sweet Ellen Joyce'