Probs with bidders bidding very high on my items and then not paying.

[suzukimifsud]

I have had 3 ebayers so far bidding on my items very high to make sure they win and then dont pay. I try making contact with them while they are still bidding on my other items and they dont respond! how do i stop this from happening, they even go to the extream to make sure i cant relist the item straight away. How do i stop new and old ebayers with no feedback score