Be firm and start by laying these two little gems on them and the buyers post sale rude email that your terms and conditions re handling time were not good enough

http://pages.ebay.com.au/help/buy/safe-trading.html#bidding

Before bidding or buying

Before you bid or buy, make sure you’re comfortable with the listing and the seller. Your bid or use of Buy It Now is a commitment to purchase the item. 

Evaluate the listing

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  Review the postage terms, refund and return policy, and other terms and conditions

  
  
  
  


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  Make sure that you’re eligible to bid on or buy the item.

  
  

   

  
  

  http://pages.ebay.com.au/help/policies/buyer-rules-overview.html

  
  

   

  
  

  Buyers cannot

  
  

   

  
  

  Bid on or buy an item when they do not meet the seller’s terms as outlined in the item listing, or bid or buy with the intention of disrupting a listing. This is known as unwelcome and malicious buying.