To prevent scammers you have to enable buyer block options from My eBay. There's info here:
http://pages.ebay.in/help/sell/buyer-requirements.html
You need this info:
http://members.ebay.co.uk/ws/eBayISAPI.dll?ViewUserPage&userid=redalligator1
http://www.macklin1.freeserve.co.uk/nigeria.htm
A third-party service, ReliaBid, can be used to avoid the problem with non-paying bidders all together. They offer a seal that acts as a deterrent to ensure that those who bid on your auctions are committed buyers. A free 30-day trial membership is available by visiting ReliaBid online at www.reliabid.com.
