I think it's silly to get that angry over an 
offer. Some people are smart shoppers, and some 
aren't.  Since I don't know the cel or the price, 
it is possible, in today's market, that a cel 
like that might only sell for 1/3 what you paid 
for it.  Some people will pay incredible prices- 
a cel that goes for $200 on one dealer's site may 
have another from the sequence priced 2 or 3 
times that on another dealer's site.  A really 
good example of this is Ah my Goddess Movie cels 
and Ayashi no Ceres cels.  Both have come down a 
lot in price from when they first came out- Anc 
cels that sold for $300 or so are now fetching 
$75 - $100.  Cel prices go up and down, it 
happens.