I buy things from ebay from time to time. I have never bought from craigslist.
I just bought a "custom" 41cm Gunnar Sport frame with a Reynolds Ouzo Pro fork on ebay for ~$250. Looks like someone had it made for themself and it didn't work for them for one reason or another. I was thinking of getting a custom Sport made for myself; the frame alone is $1000+. This one I got is the exact size I'd have made. The fit is perfect and the ride quality of this frame is outstanding. (I'll post more on this bike, with pics, later.)
When I saw the auction, I knew what it was and I put a stupidly high max bid to make sure I'd get it. It went for a lot less than I thought it would.
When buying on ebay its a good idea to know exactly what you want so you can recognize it when an auction comes up. I have several saved searches on ebay for items I'm looking for. I get emailed when an auction fitting that description comes up. Like, I have a Gunnar saved search.
Specialized Ruby
Gunnar Sport
Salsa Vaya Ti
Novara Randonee x2
Motobecane Fantom CXX (Surly Crosscheck)
Jamis Dragon