The transaction has been reported to Microsoft with key code and the seller's id name and address. So if it's bogus, Microsoft should notify me so I'm able to obtain a refund.

If the license is revoked I'll be requesting a refund from the seller. If the seller won't issue a refund the transaction based on return details this item is covered by eBay Money Back Guarantee

eBay in the past has issues refunds themselves on items where there were problems with a seller issuing a refund. Most of them ended up losing their eBay membership. I suppose if what you say about the software is true Microsoft potentially could sue and/or open a criminal or civil case against the seller.