I'm trying to sell a Laptop on ebay (450 quid, Toshiba centrino brand new with warranty etc if anyone wants )

I keep getting bidders at the last minute which are scams, ie i will pay via postal order, im Nigerian, my assistant will collect when he has finished blowing me bla bla bla.

I've put on the ad, no foriegn bidders, and noone with no feedback.

How can i stop this?