I went along to my local (well, nearest) police station and reported theft and fraud etc.
They located the seller, went round to his house and spoke to his mum. The arrival of the police at the mum's house in a small Welsh village was more effective than a 12 bore!
Since then, I've not worried that the police 'won't be interested'. I suggest that, rather than moan in anticipation that they aren't, we give them the chance to show that they are!