No no no, I wasnt meaning to buy the cel simply 
because someone wanted it and you wanted 
something of theirs.  The way I meant it was just 
to buy a cel for someone because you know they 
want it, and you plan to offer it to them right 
away for the price you paid.  Im not too keen on 
people who buy cel to barter with either, mainly 
because Id hate it if someone did that to me.  
I've also done a "trade" like you mentioned 
above.  My second Nuriko cel I did that with.  I 
had someone offer it to me, but they only wanted 
to trade.  I didnt have anything at the time she 
wanted, so I waited for her to pick out something 
she wanted.  I then bought it for her, and we 
traded ^_^.  (wow, I really should be working...)