Hmm! I don't think anybody suggested eBay was an 'authorised' seller or that they were 'downloading' software from eBay or a seller on eBay.
Certainly from my point of view I would not buy anything in terms of software that did not come in an official retail box with all the barcodes and security devices you would find on a box in a retail (authorised) store.
Still some here (Mr. Hunt) will still assume if you purchased from a retailer that you found via eBay then you are dealing in pirated software even though the product activates on installation and Adobe are happy the serial number is legit
David