Have a read of message #3 on the following thread from a few months back

http://community.ebay.com.au/t5/Selling/Lame-excuses-from-buyers/m-p/341707#M30699

Send the 'buyer' a similar message and be done with them.  I would do the UnPaid Item case to get my Final Value Fees back and to stop them from leaving any feedback.