Rosie has good advice. Go with a seller who has made a lot of transactions and you have a better chance of getting your machine well packaged. Also beware if they have a very low shipping amount. It just isn't inexpensive to have a sewing machine shipped.
I bought a Featherweight on Ebay and it is a great machine that I got for a good price. Just choose your seller carefully and you have a better chance for success.