I like the idea, although I think the management of an auction site is more labor intensive than we realize. What happens if people don't pay? Who will administer all the botched transactions? Are you sure you are getting the top price if only OG members see it and not the full ebay audience? Just some questions that come to mind. :)
One thing Ive noticed and like about this site is some members put members here first before they put something on ebay. I like the devotion that these sellers have here.
We have the Buy Sell Trade section. Here people can deal with each other on their own terms instead of one set of terms like a formalized auction site has. Sometimes a formal structured approach might be better. That is what ebay and other auction sites are for. Sometimes it is better if the two participants negotiate a deal or the buyer or seller dictates the terms under which they are willing to deal with others.
If you make this site more formal, then many of the problems that some have with ebay such as payment method will show up here. Also, the cost and effort of managing this would probably lead to costs being applied to transactions. The cost would liely be higher or money losing for the site owner because of the economy of scales working in reverse. Better to keep this site informal and open ended since ebay or other auction sites will always be there for us so that the buyers or sellers always have multiple options.
You could post what you want to sell in an informal auction and tell your prospective buyers to list what they are willing to bid in a process which ends at a time which you decide under your terms - payment, shipping, etc.