I run much the same type of series as you, except it isn't a house concert series because none of the organizers have the necessary space in their homes. A local synagogue offered us the use of their space, and it is working out very well. We state clearly on our website that while we have no objection to folk, rock, pop, or singer sonwriters, our series was founded specifically to provide a venue for traditional music, and that's the type of act we will be booking.   We don't get into any debates about what traditional music is - since it's our series we get to decide what fits and what doesn't. We've had a few people who questioned this, but if we've politely declined, we don't feel compelled to answer any arguments. In one case, a person who we considered to be a singer songwriter insisted that his roots were traditional and he was trying to get back into it. He invited us to one of his performances which wasn't too far away. We went, he did a beautiful all traditional set, and we booked him. That was Dana Robinson (along with his wife, Susan). So, we are not inflexible - but we do stick to our original mission, which is to provide a venue for traditional music. So far we are pulling in an audience, so it seems like we are doing something right.