Sedo and Ebay are advertising venues first and foremost ... to the best of my knowledge, they are NOT auction houses, NOT licensed auctioneers, NOT licensed brokers, NOT escrow agents, etc...
Bottom line is that one counts their lucky stars when Sedo, Ebay, etc work as one expects for large dollar transactions, but often it seems that the exception not the rule ... fake sales, canceled transactions, shill bidders, etc is about par for the course for those places.
There's definitely a window of opportunity for sales venues that can innovate to the next level ... ie. verification of listings, along with buyers and sellers, more intuitive interface, etc ... Snapnames and some other drop auction sites are well positioned to dominate the auction space if they play things right.
Ron