I also had this same thing happen to me once.  I 
think just about everyone has.  I had sold a rare 
manga to a younger girl, or, so she said, on 
Ebay.  She told me her mother had to get the 
money order for her, so the payment would take a 
long time.....

2 months later, I had never gotten a payment.  
She begged for me not to sell the book again, 
but, I had to in the end.  I was also in need of 
money at the time, and it puts you in a very bad 
position when someone doesnt pay you.  Part of 
you wants to be cool, and give the person a 
break.  But, the other part of you knows you need 
the money.  Even if they are a friend, or a well 
known customer, they have a responsability to pay 
you for their order.  I also think you should 
make a last attepmt to contact this person.  Be 
as nice as you can, the customer is always 
right...well, I like to believe that, but it's 
not always true.  I have gotten mad at things 
like this before, and it makes for a very bad 
situation.  Making enemies is not a good thing in 
this hobby. I know some perfectly good people who 
are into cel collecting, who have been totally 
ruined just for getting into a trifle of a 
misunderstanding between a seller or buyer.  So, 
be polite if you write them, and ask them what 
the deal is going to be.  If they dont answer you 
responsibly, then I think you should sell the cel 
to another home.  I am sure someone will 
appreciate it, and give you the money you need.

War is too great a cost most of the time....note 
my name, it says it all :)  Good luck,

Pyrrhusgirl