This is a prime example of why I think 
making/taking offers is a shady practice and I 
avoid it whenever I can.  It's a big game I'd 
rather avoid - the seller obviously knows what 
amount they would accept, but keeps it a secret, 
hoping the buyer might throw out an even higher 
amount and they could make a few extra bucks 
than if they were just honest to begin with.  

So, you don't tell him what you'd want in hope 
he'd offer high, and he offered low in hopes you 
would take it.  I don't see the difference so I 
don't think any kind of nasty response is 
warranted.  

No one has any way of knowing what you paid for 
the cel unless you have it listed there, and 
cels are worth different amounts to different 
people.  I'm sure there are people who wouldn't 
pay $10 for Yukito cels I'd pay $100 for, for 
example.  It depends on the person's interests.  
And, I paid $20 for a cel from the same sequence 
another paid $150 for, and it looks almost 
identical; so while someone offering me $50 for 
it would be a nice price, that would be 
an 'insult' to the other person, right?  How 
would that buyer have any idea about that?

I don't think spending 2 minutes reading a 
couple emails from this person wasted so much 
time that it deserved a nasty email..  You guys 
could have responded with the price you *would* 
accept, after all, who's to say he wouldn't have 
offered more?  It blowed my mind the few times I 
made an offer in the past (on cels that were 
specifically up for offers, not just some cel in 
a gallery that I liked) and the seller just 
said, "Sorry" with such finality and a hint of 
insult, when I was ready to pay more if they 
would've just been honest.  Well, they lost a 
customer, I didn't send a re-offer with that 
kind of attitude.  

And I think thats all you've accomplished 
here... lost a potential customer, and as 
someone else said, lost a potential 
seller/trader as well, should they wind up with 
anything *you* want from them.  *sigh*