I don't mind buying from auction sites, because I look at 
it as a way to insure that the person who wants it most 
gets it. Sure, the price may be higher than buying 
directly, but if Nichibei had put the Kunzite cel I won 
from ebay up on their site first, there was no way someone 
else wouldn't have ordered it before me.  But via ebay, I 
wanted it more, and by paying more was able to get it.
  Some might argue "well what if you don't have the money 
to pay those prices" but if you're in this hobby at all, 
you obviously aren't dirt poor, and if you really want that cel up there bad enough, you can always sell off some of 
your other cels to get it.

Which brings me to the issue of selling. I use ebay a lot 
to sell my cels, however it is not my first choice for how 
to do so.  You have to pay a fee, and it takes longer 
because you have to wait out the auction.  All in all I 
prefer direct sale, but you reach a larger market with 
ebay, and therefore have a better chance of finding a 
buyer.  Generally when I want to sell something, I will put
 it up for direct sale off my site for a day or two, and if 
nobody bites I will then put it up on ebay.