Tara's answer is right on the money.  Here's some 
more thoughts.

The forum crowd is a more educated and (generally) 
less flaky crowd than Ebay.  So you can count on 
speedy responses and quick payment, relatively 
speaking.  By the same token, people on her know 
what cels are worth and are accustomed to bargain 
hunting.  You will NOT get top dollar here.

EXCEPTION: Really expensive cels will do well 
here, since you are most likely to find the type 
of collectors that specialize in that particular 
character or series.  It's like offering a Rolls 
Royce at Wal-Mart (Ebay) or here (import car 
showroom).

If you don't mind waiting longer for transactions 
to end, and taking a chance on flaky buyers, you 
will get the best prices if you sell mid to low 
range cels on Ebay.  And as long as you advertise 
on here, you will still get forum bidders bidding 
on Ebay as well.  (Beware of placing hidden 
reserves on your auctions as many people, myself 
included, avoid auctions with reserves.)

Taking offers on cels rarely works, unless you 
KNOW the cel or cels are in high demand.  However, 
if you are like me and have a hard time putting 
prices on cels, you can always set up a limited 
time frame for offers, with a clearly stated 
minimum.  For example, "I'll take offers until 
Friday night, minimum is $20."

One final thing to consider.  Although I have sold 
cels all three ways---Ebay auctions, sale page 
advertised here, and private sale---there are 
peripheral benefits to offering reasonable prices 
on a sale page open to the forum, mainly in the 
forms of karma and good will.  If you offer good 
deals to other collectors, it may not pay off in 
immediate profits, but it may open the door for a 
great deal on a cel that you want in the future.  
;-)

JP

PS--Sneaky Ebay observation.  I've experimented 
with this, so I know it's true.  If anyone wants 
to complain, don't bother.  I'm just stating a 
fact from my personal experience.  If you want to 
put some cels on Ebay with somewhat reasonable Buy 
It Now prices, don't always advertise here first. 
 If other collectors have first crack at cels, you 
will see a lot more of them go for the minimum 
bid.  Pure Ebay shoppers will be more likely to 
use the Buy It Now feature.  (The exception would 
be if you put cheap BIN prices on them, in which 
case I DO advertise here first to give folks first 
crack at the good deals.)  ;-)