If you have an ebay account, you can sometimes 
use that to your advantage. Simply post the 
descriptions of the cels you are selling on a few 
boards(Cel#, scene, episode and characters 
depicted). Then, give them a link to your ebay 
account feedback. If a seller doesn't have a pic, 
but has good feedback then I am more likely to 
believe him/her. Also, use paypal so people can 
pay for them. It is much easier than using a 
money order and they know that getting their 
money back is going to be easier if they need to. 
Just a couple of suggestions.