Ah, for an investment like that, I would go straight to Sonnet and purchase from them.
eBay is for trinkets and collectibles, not computer parts (since they're so volatile), unless you've got money to spare, since it's damn tough getting a seller to take a return or give a refund. The people on eBay have no credit, and just because they've got a high seller rating doesn't mean that they're legit!
Contact whomever you purchased it from and explain what's going on.