The whole 'cans for votes', leafleting, spamming, etc makes the prize meaningless anyway. Pretty sure you know if your establishment is better than Dave's Plaice or not.
Why not suggest to the organisers that campaigning be limited to posters on display in shops? Easy to monitor and just disqualify anyone who transgresses.
I think this is entirely up to the organiser what's the rules are stated before the contest started . For example if , the national Election Day is up , they can't stop any politic party to campaign to get their votes . Thanks anyway for voting . I think I been rigged !!