Look a the email you recieve - does it come from the right address i.e. eBay.CO.UK for UK auctions or .COM for American ones.
How do they want paying? Western Union? Forget it - Western Union is a CASH transfer system for transfering CASH to people you KNOW! Once they have the code western union gives you - they can get the cash out - NO REFUNDS!
Is the Offer too good to be true? If it is - It probably isnt!! Does he charge VAT? Ask for a Vat number
Where is he? Look at the details ebay give you - if they say Wales & he gives you an address in Scotland - Ask the Question....
Ask for a phone number - A recent one that tried it on with me, said he was deaf because of a recent accident - Hmmm, That and the fact that he wanted Western Union payment instead of Cash on Delivery suggested that he might not have been telling the truith.
The main point is - USE YOUR COMMON SENSE - Its your money on the line - once its been sent by whatever means - its gone - Make sure you get what you pay for..