Our local folk club has a clause in the contract when we set up concerts for other performers that any other performances within 60 days and 25 miles of the center of our city are not permitted without the expressed approval of our organization.We generally offer our approval to perform at venues that we know from experience don't impact much on our audience (a local stage whose audience is mainly made up of tour-bus patrons, for example) or for events which seem like good "teasers"--likely to generate interest without dispelling it and thereby boost attendance at our sponsored event (a short set as a part of a large crowd, or a radio gig., for example).
We also have an awareness of folk clubs which abut or overlap our area, and try to coordinate permission with them, too.
--Charlie Baum