Not eBay, but I purchased a white featherweight in its case off the net years ago. Most people don't know how to properly ship a sewing machine. Mine was shipped inside its case (bad, bad, bad) so it arrived with the case damaged from the machine moving inside it. I had paid for insurance, so I had to file a claim with the shipper (can't remember now which shipper it was) to get some compensation for the case. It really was the seller's problem for not packing correctly, but the shipper did pay for the damage.
I think it's okay to buy a machine off eBay provided the seller has excellent feedback. Before ever bidding, you need to email the seller to find out how the machine will be packaged. If it comes with a case, the case should be shipped as a separate package. The machine itself should be "double boxed" with lots of padding. Sellers who routinely ship machines are much more likely to know how to properly package a machine for shipment. Others may be willing to package properly once they understand the need.
Don't buy unless you can have the shipment insured.