If you purchase from eBay, make sure the seller knows how to package a sewing machine for shipment. Many, many machines are damaged in shipping because of poor packaging. If there is a cover, the machine should be shipped separately from the cover. Double boxing is good.
If you are unsure, email the seller. If they have never shipped a machine before, you may have a problem. Ask if you can purchase insurance for the shipping.
Before deciding on a machine, join some of the vintage sewing machine groups at
http://groups.yahoo.com to get a feel for the different machines.