eBay for penny auctions?

A subject that comes up in conversation (when you spend as much time talking about penny auctions as I do) is "Why isn't there a consumer-to-consumer penny auction, an eBay/Swoopo mashup?"

The dialectic goes something like this:

Socrates: Why, in all the wide world, isn't there a site where one person, not previously engaged in commerce, can offer for sale to passersby some personal possession -- and be assisted by another person, an auctioneer, that auctioneer being compensated not by the seller, but by each would-be buyer, who pays a small fee even to make an offer.

Plato: I think, Master, that auctioneer would collect the lion's share of the money -- and what man would offer his property for sale, knowing he would receive only a tiny fraction of its true worth.

Socrates: Is there no solution to that objection?

Plato: Perhaps, the auctioneer could share with seller a portion of the fees he collects?

Socrates: Is there not an epistemological problem with that proposal?

Plato: I do not understand.

Socrates: Does the auctioneer know how much a bid has earned him? Are not the bids themselves a chief stock-in-trade of the auctioneer? Each bid has been itself bought in auction, and in those auctions, bids that were bought in auction were expended, and so on.

Plato: And so on, Master, but not ad infinitum. Careful, painstaking bookkeeper would tell the auctioneer just how much was brought in by each bid and its ancestors.

Socrates: It would tell the auctioneer, but not the seller, who would have to rely on the auctioneer's diligence and honesty. And this world is full to bursting with lazy and dishonest men who would pose as auctioneers.

Plato: Perhaps the auctioneer could pay the seller some fixed price per bid expended, regardless of how much that bid truly brought. Or perhaps the auctioneer could guarantee a price for each good. Or perhaps ...

Socrates: Perhaps we have reached the limit of philosophy. Perhaps we just have to attempt it.

Plato: Perhaps.