I think you'd be best running an auction here on 
Animanga, since:

A) It's free. (No Ebay fees.) Not to mention, 
it's directly targeted at cel collectors. (If you 
worry nice cels might leave the "cel community" 
and go to some clueless goof who will tack it to 
a corkboard in their dorm room. o_0)

B) It's a way you can accept multiple bids from 
people. (Without having to do all the e-mail 
answering yourself.)

C) It lets the shy people get involved. (Yes, 
some people are just too shy or intimidated to 
write to someone they don't know well to even 
make an offer. Or uncomforatble enough with doing 
so, that they wouldn't make an offer on something 
that they otherwise might have bid on if it were 
on open auciton.)

D) There's a known *end time*. (One of the things 
I dislike the most with "offers" is that you 
never know when the person is going to get back 
to you. . . Maybe they didn't get your e-mail, 
maybe they're swamped, or maybe they're waiting 
for someone else to reply to them - all valid 
things that take time during an "offers" period. 
But it's a hassle to try to keep large sums of 
money available for an unknown length of time.)

But also - what I consider to be truly "accepting 
offers" is what you are calling "one time offers".
If you're basically pitting the offerers against 
each other until they run out of money or don't 
want to pay more, you're really just running an 
auction anyway. (I just guess I don't see the 
difference except that it takes longer through 
private e-mail. *shrug*)

But I have to say, I disagree with one thing said 
here, and that is about replying. . . Unless 
there are minimum offer amounts on the cels, I 
feel someone taking offers SHOULD to reply to 
*everyone* who sends an offer - even if it is 
under what you paid. (Think about it, mouse: How 
is anyone else supposed to know the price paid 
for a given cel? No reply lands you back with 
the: "Did my e-mail get through?" question and 
maybe someone is trying to keep their money 
available, waiting to hear back. When should they 
decide they've been silently brushed off when 
there's always the possibility of the other 
person being swamped in e-mail?)

Anyhow, the other reason I would "vote" for the 
Animanga auction is because, I don't know about 
anyone else, but I don't like making offers on 
things at all. Often, even if the someone has 
something I want, I shrug and leave if there are 
no price tags. That's just the way I am. . . (On 
the other hand, when I *DO* make an offer on 
something. . . You know I *REALLY* want it. ^_^)

Many Sharp Smiles,
--Drac