Mostly the ones on eBay are mostly used and nearly depreciated or nearing their estimated useful life which is why before you proceed in buying on those sites it's better to be cautious since we are talking about a large amount of money here and this are wallets we used to safe keep our cryptocoins so as much as possible buy on the official websites.
What do you mean by "nearing their estimated useful life"?
Of course I would definitely buy a new one, but it's a piece of electronic after all.
It doesn't degrade in a year or two
You are correct, but there are numerous reasons why it is preferred to order these devices from the manufacturer. Amazon usually has a dozen suppliers, as well as itself stocking them.