Hi
have bought 3 machines of ebay. The first 2 were featherweights and are fine. Llast winter I bought a Bernina 440QE. The seller was genuine and I just had a hunch it was all ok. I paid via paypal so that offered some protection, but I needn't have worried. we went and collected it (made sure it was feasible distance for us to drive to), and I am so pleased with it. The lady I bought it from showed me how it worked and all the attachments. She even sent on some bobbins she found about 4 months later when she had a clear out.
My experiences have been really positive, but I was very careful I don't think everyone would be so lucky. Also remember you have no warrently buying in this way. I took the risk and saved £500.