A non payer strike is what ebay puts against a bidders account if they do not pay for an item won, after you receive so many (sorry cant remember how many) strikes your account is suspended and/or closed.
Ebay can assist you by emailing the winner bidder giving them a specific amount of time to pay and if they dont then they will receive a Non Payer strike.

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Someone stole my kitchen table......Oh wait..... there it is, impersonating a pile of coupons.