I will cherry-pick a quote from another poster above:
I think it's worth the time to learn what you have so you can price by what you think fair. As for eBay, unless you have people who follow you, I wouldn't trust the auction format
And then apply it to this 1855 cover you posted in this thread:http://goscf.com/t/84322&whichpage=1#779013
It illustrates the art of selling postal history on ebay in their two major format options:
Buy-it-now: Do you have the time and interest in learning the most important aspects of this cover including the exact ID of the stamp through its plating characteristics ultimately to arrive at some price? Or ...
Auction format: Where a sale can be accomplished with minimal time/knowledge investment yet still reach the majority of those who will be interested and reach an honest sale price.
Consider a listing with 3 good scans: the whole cover, a close-up of the stamp and a scan of the contents accompanied by a written description along the lines of "1855 folded cover with imperforate 1851 issue adhesive stamp with bottom sheet margin, not plated for exact ID, but will be a Scott 10, 10A, 11, or 11A. Lengthy letter headed Red Fork, Desha County, Arkansas and mailed with manuscript cancel from Napoleon Ark (both DPO) addressed to Danville, Kentucky. Sender is XxxxX, recipient is YyyyY with interesting content of the letter mentions ...."
With all the threads/posts in this forum, any ebay lots with the words 1851, plated, 10, 10A, 11, 11A , the geographic connections, etc., will be found by the potential buyers who have creative and extensive searches built to find stamps/covers in their areas of interest. Start the bidding at 9.99 and sit back.