I remember this happening at a folk festival in Scotland once - the band went out busking in the main street the day before the show they'd been booked to do. They played all their numbers over the course of an hour or two in the street, made a lot of ready cash, and nobody needed to pay to see them the next night.

The big names have proximity clauses levied on them, not to play within say 50 miles of the venue within a month, or something like that. It may seem a bit high-handed to insert a proximity clause in a booking agreement at local-gig level, but if you're paying a fair whack for a band, I think it's justified. - Ian B