Your bid can be blocked by the item's seller if he doesn't want to sell to you. There may be several reasons why:
- You don't live in the seller's country
- You received a premonition because of a not paid item
- You don't have a PayPal account
- You received too many negative ratings
If you've already acted as seller on eBay you can find the criteria by which bidders can be blocked in:
'My Account' -> 'Preferences' -> 'Buyer Requirements'
Access the accordant eBay help pages here:
http://pages.ebay.com/help/sell/buyer-requirements.html