Thing is, ebay spends most of it's advertising in google...that's what I read a while back. Google potentially has the power to control the internets traffic (if for example they started advertising their own marketplace in google).

You could imagine threads being posted on forums across the net very quickly, "Have you seen gmarket!!!!" or whatever it's called.....I think as big as ebay is currently, it wouldn't honestly take that long for googles version to be as big or even bigger than ebay is.