There's an easy way to avoid problems like the one you mentioned about a band mentioning where they are playing next in a competitor's place of business. Many bands that I have seen have a newsletter including a gig schedule that they bring to gigs and distribute to those who are interested in the band's schedule and origins. Also, if there were enough witnesses to see this club owner damage the band's equipment out of malice, the band could have taken the club owner to small claims court, sued for damages and probably won. A slip of the lip is no excuse to damage property (at least in a court of law anyway).