In most of these cases buyers are seeking COD options.
What you should do and which has worked for me in the past is, Put a big bold line in your listing like 'Cash On Delivery is not available' or something like that.
Make sure you make that line fat enough so that it won't go unnoticed. This will certainly reduce the unpaid items.
On ebay there's no going away with unpaid buyers, you'll still have to open the cases now and then.