There is a guy in San Diego named Jon Isaacs who does this regularly. He gets some GREAT deals - as you mentioned, from posers who bought an expensive bike and it pretty much sat there, or has a minor repair needed. Jon now has LOTS of bikes (you can never have too many). BUT, he really knows what he is doing and can easily recognize a bike that has quality components that are not worn out and a good frame.

Jon hangs out on rec.bicycles.rides and rec.bicycles.misc on USENET. He is a friendly, knowledgeable type of guy who does not mind sharing his ideas. You might give him a shot. If you want, I also have his email. Of course, as always, there will be a number of folks on this forum who can also give you the inside dope.