I have SOLD lots of machines on ebay! THere are some KEY questions.
1- does the machine RUN...
2- is the bobbin race/case in tack
3- will they ship via UPS
4- will they insure for FULL value
most on ebay don't sew, so no nothing about the machine, if you can ask a few simple questions, you can usually tell from the answers and/or the pictures they have if the machine is really something worth getting!
there are machine dealers on ebay. so try to catch a machine from one of them to be on the safest side!