Just an idea, how about make it a bidding classified add site? This would generate more viewings and also ensure the seller is getting the maximum amount of money for his item. Just a thought
Could have a new take on the ebay senario, a closed bidding system. People are allowed 1 max bid for any item. the person with the highest max closed bid at the end of the allotted time frame wins the item and thus pays to complete the transaction